[Edit: Thank you to Yochanan for moving my post here]
The matrix-synapse package is much further ahead on Arch at this point, and it just came up in the Synapse support channel that someone was unable to join a room because of their homeserver being too out of date. It’d be really cool if this package could be brought up to 1.21.2-1 or 1.22.1-1 (from 1.11.0-1). Cheers!