I am packaging greetd for Guix, which uses an atypical directory structure.When I run greetd with
greetd --config /gnu/store/xc4qf85kjq35blif08kh7h8vd703vysb-config.toml
(which is a valid config), and /etc/greetd/config.toml doesn't exist, greetd will error saying "No such file or directory". If it does exist as an invalid config, it will error parsing it. If it exists as a valid config, it is read, but apparently ignored, and the file passed to --config is correctly used anyway.
As a reminder, from our IRC conversation, your theory was the worker process spawned by greetd reads the config from the default path, but doesn't make any use of it.
Try to give master a shot. https://git.sr.ht/~kennylevinsen/greetd/commit/0d8812c80b2b61d5bd5bbd19b503459ff85ce7ff should have fixed the issue.