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

Calculating dependencies ... done!
Dependency resolution took 0.90 s (backtrack: 0/20).


!!! The ebuild selected to satisfy ">=gnome-base/gdm-45.0.1" 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 )

(dependency required by "gnome-base/gnome-45.2::gentoo" [ebuild])
(dependency required by "=gnome-base/gnome-45.2" [argument])