From the AUR (which is officially not supported)?
That package is flagged out of date, and is entirely unrequired for PRIME systems to use GDM.
If you have no other options you should probably look here and undo what you have done…
(or it may be simpler/faster to just start over … as its a new system anyways … then again if you have multiple systems, and this disk is now entirely encrypted as well as broken … then …)