Hooray, greetd has been merged! [1] However, according to upstream the greeter user only needs to be in the video and greeter groups. [2]
Whereas the guix definition for the greeter user has many more groups: (define %greetd-accounts (list (user-account (name "greeter") (group "wheel") (supplementary-groups '("users" "tty" "input" "video" "audio")) (system? #t)))) I can understand the need for tty and input, but why does the greeter user need the wheel and audio? 1. https://issues.guix.gnu.org/49969 2. https://git.sr.ht/~kennylevinsen/greetd/#manually-from-source