[Stable Update] 2020-12-30 - Kernels, KDE, Cinnamon, LibreOffice, Python 3.9, Mesa 20.3.1

[gfunk]

see this page, might not be the same issue but will help you troubleshoot:

Failed to start light display manager, tried basic forum posts

Hey guys A bit late here but updated my system and had the same issue… Idiot pamac tried to install 5.10 kernel AND linux-latest kernel (also 5.10) and I think linux-latest won the fight… I removed both then just installed 5.10 (5.10.2.2) and the issue is gone so I’m guessing they fixed it in a point update, no need to edit mkinitcpio, checked mine and the amdgpu entry is not in there