Hope no one takes this personally, I'm just stating facts here.
If we're at the "contributions welcome for foobar project" I think that indeed, most games have their own infrastructure, based either on self-hosting like openMW (ok, not a game but an engine), xonotic (game), widelands, unvanquished (game+wannabe engine, yes I allow myself to be sarcastic on this one), widelands (game), red-eclipse2 (game, via github), and blue-nebula (game) got some discussions about using github for that recently, and no one can blame them, they got locked because low activity, which is something that happen on low contribution projects but makes this place hardly reliable (low people involved means there can be pauses, especially on projects which are that mature). One of the devs (not me since not active there anymore) noticed that red-eclipse 2 seems to have a rather successful move to github discussions and not every FOSS dev is a fanatic... Wesnoth (game, arguably engine considering the 4x total conversion game mod they also have) have their forum, and the list can go on and on.
Many of those even have forums tailored to their websites and well integrated with their IRC/matrix/discord/whatever (xonotic, widelands, openmw, unvanquished, at least).
There is also a direct competitor in the name of "game dev" or something like that, on which I stumble upon from time to time when searching for stuff (needless to say, this never happens for freegamedev, but hey, the technical content here, especially on new forum, is hardly existent), and of course the stack overflow which is entirely dedicated to technical (including technics of artistic content, i.e. blender) which have bigger communities better focused on their topic.
Here, the only stuff that is both FOSS and technical that I usually see is stuff from drummyfish about his libs (that I admit I still have to check if that I could make use of, seems promising after all). Otherwise it's people presenting their games or ideas... Presenting their games is nice, ofc. Presenting one's ideas while waiting for someone to pick them up is of dubious interest, but at least they don't annoy people writing games into building their desired game for free in the meantime :D (which happens to me fairly often, speccing being a champion of that, while several unvanquished players also do that when they spot me, leading me to change nick in-game from time to time to get some peace).
Many things discussed here seems about gamejams in the end, which might be fun (dunno, never tried) and are certainly games, but it's not like there is any content about what people used to go faster or the ideas they tried in the process of making their games, only some results (often through links) which are of limited value on a community point of view (according to me, I'm sure many will disagree).