Can confirm it works on 0xchat. I setup a relay on nodana.io to test (takes a few seconds, costs a few cents per day, can stop anytime). Then I created a few accounts on 0x chat and added that relay only (app relay and DM relay, ignore inbox and outbox relays), and works fine with both MLS and NIP 17 chats. Just have to be on the right version both phones. Or you can use a single phone with app in the right version and swap between test accounts.