This the strongest argument against building a community on top of proprietary services, especially if's a startup / VC money is involved. It's guaranteed to enshittify / sell out to a big company, and your community will crumble.

That being said, I am guilty of helping building Zig communities on Discord, but in my defense none (literally none) of the FOSS alternatives was good enough at the time. And I'm also not really happy with plenty of the newer ones.

I'm now working on my own take of what an open source Discord alternative should look like and I plan to move away from Discord by the end of the year. You can find it on codeberg, it's called awebo, I'm intentionally not posting a link since these are super early days.

On the other hand, these platforms are free and much easier to work with, especially for non-technical administrators.

As of today, there just doesn't seem to be any good simple forum software. They all seem to need quite a bit of upkeep.

Campfire by 37Signals [0] might be interesting to you. This can also serve as a foundation to add your own features on top of.

[0] https://once.com/campfire

I'm guessing you looked at matrix and decided it wasn't suitable?