Can't login with X11 - which package to install?

Is this with AMD GPU? Quite unclear, also not present on your user description, hence i only speculate that you might have to make use of early KMS Kernel mode setting - ArchWiki
add inside /etc/mkinitcpio.conf to the MODULES line:

MODULES=(amdgpu)

But probably best to share more info about your system, as described here: