Unmask all packages in Gentoo for a specific ISA:
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In the /etc/portage/make.conf file, add this to the end of the file to unmask all packages (replace ppc with your wanted ISA, and keep the ~ before it):

ACCEPT_KEYWORDS="~ppc" ACCEPT_LICENSE="*"

Source: https://www.reddit.com/r/Gentoo/comments/t64ge4/how_to_unmask_this_package/
Date: May 6th 2023