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

Calculating dependencies ...

!!! Problem resolving dependencies for =gnome-base/gdm-48.0-r2
 done!
Dependency resolution took 0.82 s (backtrack: 0/20).


!!! The ebuild selected to satisfy "=gnome-base/gdm-48.0-r2" has unmet requirements.
- gnome-base/gdm-48.0-r2::gentoo USE="X -accessibility -audit -bluetooth-sound -branding -elogind -fprint -plymouth (-selinux) (-systemd) -tcpd -test -wayland"

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

  The above constraints are a subset of the following complete expression:
    exactly-one-of ( elogind systemd ) any-of ( wayland X )