The main Matrix homeserver (matrix.org) is down and likely to remain down for a while longer:

https://mastodon.matrix.org/@matrix/115135992360783162

Our Matrix rooms are still available since those aren't hosted on any specific server. We use our own Matrix server for our project accounts, bridge bot, etc. too.

Our chat rooms are bridged across Matrix, Discord, Telegram and IRC.

Discord server: https://discord.com/invite/grapheneos

IRC channels are on libera.chat with the same names as the Matrix rooms but prefixed with #grapheneos such as #grapheneos-offtopic. #grapheneos-general redirects to #grapheneos there.

Our chat rooms were only on Matrix after the end of freenode but we ended up needing alternatives due to both the technical and abuse issues with Matrix. Discord is now the most active. Long term, we plan to self-host a future high quality open source Discord clone and drop Matrix/Telegram/IRC.

Our Telegram group is https://t.me/GrapheneOS but we recently set it to require requesting to join and being approved by a moderator due to the massive issues with spam. We recommend joining our chat rooms via either a non-matrix.org Matrix server (even after it's back, it's too large) or Discord instead.