Just received another update, for manjaro-system. I got the following error when upgrading
==> Fixing Nvidia drivers
error: failed to init transaction (unable to lock database)
Error while configuring manjaro-system
error: could not lock database: File exists
Error while configuring manjaro-system
if you’re sure a package manager is not already
running, you can remove /var/lib/pacman/db.lck
Hopefully fixed …
Yep all fixed 
i got this as well, then another manjaro-system update was just pushed and it times out when try to build and get a daemon error:
get_authorization: Timeout was reached
remove_authorization: Timeout was reached
Black screen after login screen,following update. was using Kernal 5.10.4-1.
Dowgraded to Kernal 5.9.16-1, fixed the error, will try 5.10.4.1 after next major kernel update. Unless the is a fix?
Operating System: Manjaro Linux
KDE Plasma Version: 5.20.4
KDE Frameworks Version: 5.78.0
Qt Version: 5.15.2
Kernel Version: 5.9.16-1-MANJARO
OS Type: 64-bit
Processors: 4 × Intel® Core™ i5-7300U CPU @ 2.60GHz
Memory: 15.5 GiB of RAM
Graphics Processor: Mesa Intel® HD Graphics 620
Have seen a earlier post @ AMD graphics, I am having same problem on Intel graphics?
xfce4-power-manager Panel icon is broken,
Show Desktop icon is blue.
Some Papirus icons not Themed as expected
VMware Workstation too 
this was fixed for me after a reboot:
Preparing…
Synchronizing package databases…
Resolving dependencies…
Checking inter-conflicts…
Resolving dependencies…
Checking inter-conflicts…
Download of manjaro-system (20201231-7) started
Download of manjaro-system (20201231-7) finished
Checking keyring…
Checking integrity…
Loading packages files…
Checking file conflicts…
Checking available disk space…
Upgrading manjaro-system (20201231-2 -> 20201231-7)…
==> Checking if Nvidia drivers need an update …
Running post-transaction hooks…
Arming ConditionNeedsUpdate…
Checking which packages need to be rebuilt
parallel: Warning: $HOME not set. Using /tmp.
Transaction successfully finished.
If you switch to 5.10 is linux510-nvidia being shown if you do a pacman -Q | grep nvidia ?
No, but I do get a list of some Nvidia drivers
~ >>> pacman -Q | grep nvidia
lib32-nvidia-utils 455.45.01-3
linux59-nvidia-455xx 455.45.01-4
mhwd-nvidia 455.45.01-3
mhwd-nvidia-340xx 340.108-1
mhwd-nvidia-390xx 390.138-1
nvidia-455xx-utils 455.45.01-1
nvidia-prime 1.0-4
opencl-nvidia 455.45.01-2
There’s only one driver there, linux59-nvidia-455xx but it should be linux59-nvidia by now 
So there’s your “module problem” you don’t have linux510-nvidia installed and you come from stable where it is not available as I see, so makes sense
Normally it should be fetched from the extramodules but seems not the case with you, you could try “mwhd-force-installing” your drivers again while in 5.10 and see if it’s there or in the worst case you could install it alone, in any case you should have 5.4 LTS installed for fallback if something wouldn’t go right, as I also see that you don’t have the “linux54-nvidia” as well.
But some explanation on the above (missing in stable but not in testing) maybe from @nightmare-2021 would be nice 
In case anyone had the same problem as me (black screen after grub), once you are on the black screen ctrl+alt+f3 and run “sudo pacman -Syu” again to install the most recent manjaro-system then reboot. Then in grub change kernel to 5.9, and once again boot. If you don’t get into your GUI then press ctrl+alt+f3 and then run “startx”
Feel like my problem was caused by my own ineptitude but if you are similarly inept then i hope this is helpful.
But that’s not bad, I’m testing in the VM, the packages have to be readjusted etc. that can take a while 
Just updated, no major issues so far. The xfce4 power icon in the tray is broken, appearing with the wrong colour.
The updates to the manjaro-system package (2 last night, 1 this morning) complaing about broken nvidia drivers (missing 455, although the correct video-nvidia driver is installed). Nvidia drivers and optimus-switch are both working regardless.
The latest manjaro-system update (20210101-2) did not output errors regarding nvidia, altought it gave
(1/1) upgrading manjaro-system [-----------------------------------------------------] 100%
error: command failed to execute correctly
after which no other errors or aditional information were given.
Thanks for the info.
I have learned that I really don’t know how to use mhwd properly (especially when trying to use -f), BUT I managed to get one method correct, but it throws an interesting error.
~ >>> sudo mhwd -i pci linux510-nvidia
[sudo] password for olividir:
Error: config 'linux510-nvidia' does not exist!
Testing branch.
:: Synchronising package databases...
core 168.6 KiB 1441 KiB/s 00:00 [####################################################################] 100%
extra 1977.9 KiB 2.94 MiB/s 00:01 [####################################################################] 100%
community is up to date
multilib is up to date
:: Some packages should be upgraded first...
resolving dependencies...
looking for conflicting packages...
Package (1) Old Version New Version Net Change Download Size
core/manjaro-system 20210101-1 20210101-2 0.00 MiB 0.02 MiB
Total Download Size: 0.02 MiB
Total Installed Size: 0.00 MiB
Net Upgrade Size: 0.00 MiB
:: Proceed with installation? [Y/n]
:: Retrieving packages...
manjaro-system-20210101-2-any 21.0 KiB 0.00 B/s 00:00 [####################################################################] 100%
(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%
:: Processing package changes...
(1/1) upgrading manjaro-system [####################################################################] 100%
error: command failed to execute correctly
:: Running post-transaction hooks...
(1/1) Arming ConditionNeedsUpdate...
:: Starting full system upgrade...
resolving dependencies...
looking for conflicting packages...
Package (1) Old Version New Version Net Change Download Size
extra/sddm 0.19.0-2.2 0.19.0-2.3 0.00 MiB 3.43 MiB
Total Download Size: 3.43 MiB
Total Installed Size: 4.72 MiB
Net Upgrade Size: 0.00 MiB
:: Proceed with installation? [Y/n]
Previous message was from my laptop (hybrid intel+nvidia, i3 testing branch).
Just updated my desktop (kde + nvidia, also testing branch) and had the exact same output from pacman as you have
This issue already has been logged in the Arch Linux bug tracker, FS#69154 : [xfce4-panel] Process 2079 (panel-6-systray) of user 1000 dumped core
I haven’t updated the system yet, but I do have installed linux510-nvidia 455.45.01-8 from previous updates, so the package do exists.
I also am using optimus-manager so I’m always looking out for possible nvidia issues before updating. Sometimes happens that nvidia modules are coming after the kernel update and in the meantime, nvidia won’t work. Usually, Manjaro team try to have all packages there, but sometimes things slip out.
I guess I wait a few more days with this update to be sure everything is there.