I’m kind of puzzled which ports you actually need for Nextcloud Talk.
The Nextcloud in case is behind a router that has all ports closed inbound by default. But I can open up everything individually for TCP and UDP traffic. It also has a public IPv4. So yes, it’s basically a DMZ.
I do need 80 and 443 for Nextcloud in general and they are already open. But are there any other ports that you need for Talk?
Because establishing a call right now is a little hit and miss.