Error loading QML file in System Settings

When opening manjaro system settings, certain tabs (like Global Themes/Plasma Themes/Colors/Icon) display a “Error loading QML file” error.

Here is a screenshot:

The issue started after an update a few months ago.

Did you mixed non git version with git version by chance? If you are on stable branch, the default KDE Plasma, then run this from terminal:
sudo pacman-mirrors -f5 && sudo pacman -Syyu knewstuff
Reboot after that and test again.

I ran the command you mentioned.
It asked me the replace a bunch of package (to which I said yes) and in the end it says that two packages python-gast and python-gast03 are in conflict.

::INFO Downloading mirrors from repo.manjaro.org
::INFO Using default mirror file
::INFO Querying mirrors - This may take some time
3.413 Hungary        : https://quantum-mirror.hu/mirrors/pub/manjaro/
..... Hungary        : http://quantum-mirror.hu/mirrors/pub/manjaro/
2.964 Netherlands    : https://manjaro.mirrors.lavatech.top/
1.930 Netherlands    : http://manjaro.mirrors.lavatech.top/
3.549 Russia         : https://mirror.truenetwork.ru/manjaro/
1.969 Russia         : http://mirror.truenetwork.ru/manjaro/
3.447 Pakistan       : https://repo.inara.pk/manjaro/
1.996 Pakistan       : http://repo.inara.pk/manjaro/
3.154 Germany        : https://mirror.netzspielplatz.de/manjaro/packages/
::INFO Writing mirror list
::Netherlands     : https://manjaro.mirrors.lavatech.top/stable
::Russia          : https://mirror.truenetwork.ru/manjaro/stable
::Pakistan        : https://repo.inara.pk/manjaro/stable
::Hungary         : https://quantum-mirror.hu/mirrors/pub/manjaro/stable
::Germany         : https://mirror.netzspielplatz.de/manjaro/packages/stable
::INFO Mirror list generated and saved to: /etc/pacman.d/mirrorlist
:: Synchronizing package databases...
 core                                                             167.6 KiB   211 KiB/s 00:01 [#######################################################] 100%
 extra                                                           1994.4 KiB   216 KiB/s 00:09 [#######################################################] 100%
 community                                                          6.3 MiB   337 KiB/s 00:19 [#######################################################] 100%
 multilib                                                         182.0 KiB   433 KiB/s 00:00 [#######################################################] 100%
:: Some packages should be upgraded first...
resolving dependencies...
looking for conflicting packages...

Packages (2) archlinux-keyring-20201210-1  manjaro-system-20201211-1

Total Download Size:   0.94 MiB
Total Installed Size:  1.30 MiB
Net Upgrade Size:      0.00 MiB

:: Proceed with installation? [Y/n] y
:: Retrieving packages...
 archlinux-keyring-20201210-1-any                                 939.4 KiB   526 KiB/s 00:02 [#######################################################] 100%
 manjaro-system-20201211-1-any                                     20.3 KiB  0.00   B/s 00:00 [#######################################################] 100%
(2/2) checking keys in keyring                                                                [#######################################################] 100%
(2/2) checking package integrity                                                              [#######################################################] 100%
(2/2) loading package files                                                                   [#######################################################] 100%
(2/2) checking for file conflicts                                                             [#######################################################] 100%
(2/2) checking available disk space                                                           [#######################################################] 100%
:: Processing package changes...
(1/2) upgrading archlinux-keyring                                                             [#######################################################] 100%
==> Appending keys from archlinux.gpg...
==> Locally signing trusted keys in keyring...
  -> Locally signing key D8AFDDA07A5B6EDFA7D8CCDAD6D055F927843F1C...
  -> Locally signing key DDB867B92AA789C165EEFA799B729B06A680C281...
  -> Locally signing key 91FFE0700E80619CEB73235CA88E23E377514E00...
  -> Locally signing key 0E8B644079F599DFC1DDC3973348882F6AC6A4C2...
  -> Locally signing key AB19265E5D7D20687D303246BA1DFB64FFF979E7...
==> Importing owner trust values...
==> Disabling revoked keys in keyring...
  -> Disabling key 8F76BEEA0289F9E1D3E229C05F946DED983D4366...
  -> Disabling key 63F395DE2D6398BBE458F281F2DBB4931985A992...
  -> Disabling key 50F33E2E5B0C3D900424ABE89BDCF497A4BBCC7F...
  -> Disabling key 27FFC4769E19F096D41D9265A04F9397CDFD6BB0...
  -> Disabling key 779CD2942629B7FA04AB8F172E89012331361F01...
  -> Disabling key 39F880E50E49A4D11341E8F939E4F17F295AFBF4...
  -> Disabling key 8840BD07FC24CB7CE394A07CCF7037A4F27FB7DA...
  -> Disabling key 5559BC1A32B8F76B3FCCD9555FA5E5544F010D48...
  -> Disabling key 0B20CA1931F5DA3A70D0F8D2EA6836E1AB441196...
  -> Disabling key 07DFD3A0BC213FA12EDC217559B3122E2FA915EC...
  -> Disabling key 4FCF887689C41B09506BE8D5F3E1D5C5D30DB0AD...
  -> Disabling key 5A2257D19FF7E1E0E415968CE62F853100F0D0F0...
  -> Disabling key D921CABED130A5690EF1896E81AF739EC0711BF1...
  -> Disabling key 7FA647CD89891DEDC060287BB9113D1ED21E1A55...
  -> Disabling key BC1FBE4D2826A0B51E47ED62E2539214C6C11350...
  -> Disabling key 4A8B17E20B88ACA61860009B5CED81B7C2E5C0D2...
  -> Disabling key 5696C003B0854206450C8E5BE613C09CB4440678...
  -> Disabling key 684148BB25B49E986A4944C55184252D824B18E8...
  -> Disabling key 8CF934E339CAD8ABF342E822E711306E3C4F88BC...
  -> Disabling key F5A361A3A13554B85E57DDDAAF7EF7873CFD4BB6...
  -> Disabling key 5E7585ADFF106BFFBBA319DC654B877A0864983E...
  -> Disabling key 65EEFE022108E2B708CBFCF7F9E712E59AF5F22A...
  -> Disabling key 40440DC037C05620984379A6761FAD69BA06C6A9...
  -> Disabling key 34C5D94FE7E7913E86DC427E7FB1A3800C84C0A5...
  -> Disabling key 1A60DC44245D06FEF90623D6EEEEE2EEEE2EEEEE...
  -> Disabling key 81D7F8241DB38BC759C80FCE3A726C6170E80477...
  -> Disabling key E7210A59715F6940CF9A4E36A001876699AD6E84...
  -> Disabling key 5357F3B111688D88C1D88119FCF2CB179205AC90...
  -> Disabling key 4D913AECD81726D9A6C74F0ADA6426DD215B37AD...
  -> Disabling key FB871F0131FEA4FB5A9192B4C8880A6406361833...
  -> Disabling key 66BD74A036D522F51DD70A3C7F2A16726521E06D...
  -> Disabling key 487EACC08557AD082088DABA1EB2638FF56C0C53...
  -> Disabling key B1F2C889CB2CCB2ADA36D963097D629E437520BD...
  -> Disabling key 9515D8A8EAB88E49BB65EDBCE6B456CAF15447D5...
  -> Disabling key 76B4192E902C0A52642C63C273B8ED52F1D357C1...
  -> Disabling key 40776A5221EF5AD468A4906D42A1DB15EC133BAD...
  -> Disabling key D4DE5ABDE2A7287644EAC7E36D1A9E70E19DAA50...
  -> Disabling key 44D4A033AC140143927397D47EFD567D4C7EA887...
==> Updating trust database...
gpg: next trustdb check due at 2021-08-02
(2/2) upgrading manjaro-system                                                                [#######################################################] 100%
:: Running post-transaction hooks...
(1/1) Arming ConditionNeedsUpdate...

:: Starting full system upgrade...
warning: bazel: ignoring package upgrade (3.5.0-1 => 3.7.1-1)
warning: cuda: ignoring package upgrade (10.0.130-2 => 11.2.0-1)
warning: cudnn: ignoring package upgrade (7.6.4.38-1 => 8.0.5.39-1)
:: Replace lib32-nvidia-430xx-utils with multilib/lib32-nvidia-utils? [Y/n] y
:: Replace lib32-opencl-nvidia-430xx with multilib/lib32-opencl-nvidia? [Y/n] y
:: Replace linux57 with community/linux-latest? [Y/n] y
:: Replace linux57-bbswitch with community/linux-latest-bbswitch? [Y/n] y
:: Replace linux58 with community/linux-latest? [Y/n] y
:: Replace linux58-bbswitch with community/linux-latest-bbswitch? [Y/n] y
:: Replace mhwd-nvidia-418xx with core/mhwd-nvidia? [Y/n] y
:: Replace mhwd-nvidia-430xx with core/mhwd-nvidia? [Y/n] y
:: Replace mhwd-nvidia-435xx with core/mhwd-nvidia? [Y/n] y
:: Replace mhwd-nvidia-440xx with core/mhwd-nvidia? [Y/n] y
:: Replace mhwd-nvidia-450xx with core/mhwd-nvidia? [Y/n] y
:: Replace mhwd-nvidia-455xx with core/mhwd-nvidia? [Y/n] y
:: Replace opencl-nvidia-430xx with extra/opencl-nvidia? [Y/n] y
resolving dependencies...
looking for conflicting packages...
error: unresolvable package conflicts detected
error: failed to prepare transaction (conflicting dependencies)
:: python-gast03 and python-gast are in conflict

EDIT: I should mention that after updating the mirrors, there is now a huge update (4 GB). I will download this update and see if it is fixed.

EDIT 2: Same error using the package manager - python-gast and python-gast03 are in conflict.

EDIT 3: I was able to remove python-gast and replace it with python-gast03.
Now it gives the following problem:

:: Synchronizing package databases...
 core                                                             167.6 KiB   309 KiB/s 00:01 [#######################################################] 100%
 extra                                                           1994.4 KiB   265 KiB/s 00:08 [#######################################################] 100%
 community                                                          6.3 MiB   153 KiB/s 00:42 [#######################################################] 100%
 multilib                                                         182.0 KiB   143 KiB/s 00:01 [#######################################################] 100%
:: Starting full system upgrade...
warning: bazel: ignoring package upgrade (3.5.0-1 => 3.7.1-1)
warning: cuda: ignoring package upgrade (10.0.130-2 => 11.2.0-1)
warning: cudnn: ignoring package upgrade (7.6.4.38-1 => 8.0.5.39-1)
:: Replace lib32-nvidia-430xx-utils with multilib/lib32-nvidia-utils? [Y/n] y
:: Replace lib32-opencl-nvidia-430xx with multilib/lib32-opencl-nvidia? [Y/n] y
:: Replace linux57 with community/linux-latest? [Y/n] y
:: Replace linux57-bbswitch with community/linux-latest-bbswitch? [Y/n] y
:: Replace linux58 with community/linux-latest? [Y/n] y
:: Replace linux58-bbswitch with community/linux-latest-bbswitch? [Y/n] y
:: Replace mhwd-nvidia-418xx with core/mhwd-nvidia? [Y/n] y
:: Replace mhwd-nvidia-430xx with core/mhwd-nvidia? [Y/n] y
:: Replace mhwd-nvidia-435xx with core/mhwd-nvidia? [Y/n] y
:: Replace mhwd-nvidia-440xx with core/mhwd-nvidia? [Y/n] y
:: Replace mhwd-nvidia-450xx with core/mhwd-nvidia? [Y/n] y
:: Replace mhwd-nvidia-455xx with core/mhwd-nvidia? [Y/n] y
:: Replace opencl-nvidia-430xx with extra/opencl-nvidia? [Y/n] y
resolving dependencies...
looking for conflicting packages...
:: threejs-sage and three.js are in conflict. Remove three.js? [y/N] y
error: failed to prepare transaction (could not satisfy dependencies)
:: removing linux57 breaks dependency 'linux57' required by linux57-nvidia-430xx
:: removing linux58 breaks dependency 'linux58' required by linux58-nvidia-430xx