• steps to reproduce:
  Install gdm in Parabola GNU/Linux-libre and log in.

• expected result:
  GDM should correctly parse /etc/motd and smoothly enter user session.

• actual result:
  GDM shows garbled text under password field and takes several seconds to log in.

This issue was already reported upstream:
https://gitlab.gnome.org/GNOME/gdm/-/issues/698
https://gitlab.gnome.org/GNOME/gdm/-/issues/718

Less experienced users may have a hard time trying to figure out what is going on here. I propose to delete /etc/motd (the way Arch Linux did) or at least modify /etc/motd to a less fancy message (I did not test this thoroughly, but simple text just works) until the issue is sorted out upstream.