This update was the biggest mess for me during all the years with Manjaro KDE. Spent 2 hours fixing it.
Update itself was fine, but after reboot I noticed ugly font and lots of wlan errors during startup, and WiFi (ASUS adapter with BCM4360 chipset) was not available. Multiple reboots and re-installation of Broadcom drivers didn’t help, so decided to switch from Kernel 5.4 to 5.10.
Couldn’t even boot to GUI on 5.10 because of TLP error - Stuck boot at "Finished TLP system startup/shutdown" new kernel Removing TLP didn’t help, still no GUI.
Back to kernel 5.4, noticed that Nvidia drivers (GeForce 1030) were marked as not installed after update (worked fine before). Trying to install them always resulted in error
nvidia-utils and nvidia-455xx-utils are in conflict
After multiple attempts I manually removed nvidia-455xx-utils and GUI instantly crashed. Reboot, no GUI again. Thankfully, I was able to re-install nvidia-utils via CLI. Right after that, GUI was live again, and drivers were marked as installed this time. Except this error:
Warning: config ‘/var/lib/mhwd/local/pci/video-nvidia-455xx/MHWDCONFIG’ is invalid!
As per @philm suggestion, removed MHWDCONFIG file and rebooted. Everything was fine, except no WiFi still. Re-installed kernel 5.10, rebooted into it, and - finally graphics and WiFI work fine (but only on 5.10, still no WiFi on 5.4).
The only remaining issue with both kernels is extremely big and blur font now - https://i.postimg.cc/NF6Ztb1b/4032-2268-max.jpg (screen size is “32”, and as you see, a short message uses alsmost all the screen space).