Ok I guess I'll have to give up again quite quickly
#Microsoft #Teams is broken for me as soon as I disable #IPv4. From what I could understand in this horrible mess of a "web app", the reason is probably some #CORS error. I have no idea how that could ever be related to #IPv6 or #NAT or anything. Tried temporarily disabling #NAT64 (to force direct v6 connections), tried adding all of Microsofts v6 networks to the "exclude" option of bind9 to have everything pass #NAT64 *avoiding* native IPv6, tried several ways to disable CORS, nothing helped.
Anyone know about these issues with teams?
edit: to clarify, "everything" seems to work except for the main purpose: join an actual call ...