@civodul i made my own client (WIP, idiosyncratic), which is probably not what you want. (ie it's more like lem.el/mastodon.el than forge)
https://codeberg.org/martianh/fj.el
see link in readme about forge/magit supporting or not foregejo.
now that i know the API a bit and a better grasp of CLOS/EIEIO, i have considered implementing it for forge.el (again, *sigh*). but i really don't have the money/time to spend the time/money on it needed at present. (i don't earn a living by using version control software!)