These are the packages that would be merged, in order:

Calculating dependencies ...

!!! Problem resolving dependencies for =gnome-base/gdm-50.3-r2
 done!
Dependency resolution took 0.83 s (backtrack: 0/20).


!!! The ebuild selected to satisfy "=gnome-base/gdm-50.3-r2" has unmet requirements.
- gnome-base/gdm-50.3-r2::gentoo USE="X -audit -branding -debug -elogind -fprint -plymouth (-selinux) (-systemd) -test" VIDEO_CARDS="-nvidia"

  The following REQUIRED_USE flag constraints are unsatisfied:
    exactly-one-of ( elogind systemd )