There's another thread showing how you can use FaceTime (simulated only) in the simulator. (Features->FaceTime) It's unclear if you can actually play as them, I think it's just to test multiple connections. You also need a paid dev account to test it on real hardware, and you need at least two units (sim <-> hardware doesn't appear to work)

Thanks. Beta 3 does work. I tried Beta 5 and it fixes that problem, but now a new problem shows up that I can't find much about: Tabletopkit Sample/GroupActivityManager.swift:26:28 Main actor-isolated value of type '() async -> Void' passed as a strongly transferred parameter; later accesses could race