It’s Discover. No, it’s not installed by default, but I don’t think it supports AUR or Flatpak.
Can my issue be related to gtk version? As I rolled back from pamac gtk4 to gtk3 as it doesn’t respect my theme.
No, it doesn’t, but you hadn’t specified that was a requirement. You see how information is important from the beginning? 
Okay, I got it. Thanks for your idea.
I know, I am sorry, that’s my fault.
I used bauh as a package manager on Arch vanilla. But, with the first update with it, it crashed, and I wasn’t able to start my system. Then, I switched to Manjaro.
Is this equal to yay command??
The same or similar syntax. The difference is that with pacman you must use sudo, when performing an upgrade, or installing a package.
Okay, I got it. Thank you for your help.
I don’t have specific problem with pamac and I continue to use it for upgrades, but I don’t upgrade AUR packages at the same time. The only time when I got problems with pamac was with a previous update (1 or 2 months ago) when something broke the sync directory.
I deleted the content of sync directory as you said. I hope this is the issue.
Can it be related to gtk version? As I rolled back from pamac gtk4 to 3, it wasn’t respecting KDE theme.
No idea about gtk version. I am on xfce and still use the gtk4 version, but indeed, it doen’t respect my global theme - and I don’t care 
.
Okay, thank you for help. It’s a little annoying to me .
I have something to try which might be related, now that you mention the theme issues, and knowing you have flatpak activated in Pamac:
sudo pacman -R xdg-desktop-portal-gnome
sudo pacman -Syyu xdg-desktop-portal-kde
There has been an issue where ‘xdg-desktop-portal-gnome’ is unintentionally installed instead of the backend specific for KDE. Theme inconsistencies are one of the symptoms.
Try that, preferably after logging out, as previously described.
I do this and upgrade to gtk4? Or without changing pamac gtk3??
Leave as is for now. You can still upgrade Pamac after, if needed.
That’s what I got:
error: target not found: xdg-desktop-portal-gnome
:: Synchronizing package databases...
core 143.1 KiB 42.9 KiB/s 00:03 [################] 100%
extra 8.5 MiB 83.9 KiB/s 01:44 [################] 100%
community 29.0 B 65.0 B/s 00:00 [################] 100%
multilib 144.2 KiB 62.2 KiB/s 00:02 [################] 100%
warning: xdg-desktop-portal-kde-5.27.8-1 is up to date -- reinstalling
:: Starting full system upgrade...
resolving dependencies...
looking for conflicting packages...
Packages (1) xdg-desktop-portal-kde-5.27.8-1
Total Installed Size: 1.02 MiB
Net Upgrade Size: 0.00 MiB
:: Proceed with installation? [Y/n]
(1/1) checking keys in keyring [################] 100%
(1/1) checking package integrity [################] 100%
(1/1) loading package files [################] 100%
(1/1) checking for file conflicts [################] 100%
(1/1) checking available disk space [################] 100%
:: Running pre-transaction hooks...
(1/1) Creating Timeshift snapshot before upgrade...
==> skipping timeshift-autosnap due skipRsyncAutosnap in /etc/timeshift-autosnap.conf set to TRUE.
:: Processing package changes...
(1/1) reinstalling xdg-desktop-portal-kde [################] 100%
:: Running post-transaction hooks...
(1/3) Arming ConditionNeedsUpdate...
(2/3) Refreshing PackageKit...
(3/3) Updating the desktop file MIME type cache...
I don’t think that xdg-desktop-portal-gnome is installed.
Good. It shouldn’t be. It was worth trying though - the output only tells us everything is as it should be with ‘xdg-desktop-portal’.
Okay, if I upgrade to pamac gtk4, will it fix the theme?
Pamac should already be gtk4 (gtk), as I understand it. Will it fix the theme? I don’t know. I’ve seen a few mentions of theme issues in the last few days, but mostly, it was due to the xdg-desktop-portal issues, which have now been corrected.
Pamac-manager (Pamac GUI) is Gtk4. Pamac-tray is Gtk3.
You might find Kvantum useful for managing themes. I’ve never used it, so I can’t say much more about it.
I tried to install pamac gtk4, but it’s still having the same theme issue. So, I rolled back to gtk3.