> Our chat rooms are bridged across Discord, Telegram and Matrix so you can choose your preferred platform.

> We have an official forum for longer form posts, which is publicly accessible and easier to search. We are using Flarum for our forum.

https://discuss.grapheneos.org/

If they mandated discord as a closed support community sure, but you can't be too upset by the mere affiliation with a discord channel when they also offer all the above