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

Calculating dependencies ... done!
Dependency resolution took 0.83 s (backtrack: 0/20).


!!! All ebuilds that could satisfy "=sys-apps/systemd-readahead-216" have been masked.
!!! One of the following masked packages is required to complete your request:
- sys-apps/systemd-readahead-216::gentoo (masked by: package.mask)
/Volumes/Disk 1/Repository/portage-git/profiles/features/split-usr/package.mask:
# Mike Gilbert <floppym@gentoo.org> (2025-06-03)
# Requires systemd.


For more information, see the MASKED PACKAGES section in the emerge
man page or refer to the Gentoo Handbook.