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

Calculating dependencies ... done!
Dependency resolution took 0.93 s (backtrack: 0/20).


!!! The ebuild selected to satisfy ">=gnome-base/gnome-settings-daemon-3" has unmet requirements.
- gnome-base/gnome-settings-daemon-50.1::gentoo USE="colord cups xwayland -debug -elogind -modemmanager -networkmanager -smartcard (-systemd) (-test)"

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

(dependency required by "gnome-extra/gnome-tweaks-46.1-r1::gentoo" [ebuild])
(dependency required by "=gnome-extra/gnome-tweaks-46.1-r1" [argument])