There have been a few cases where ports are blocked. For example on many residential port 25 is blocked. If you pay and get a static ip this often gets unblocked. Same with port 10443 on a few residential services. There's probably more but these are issues I've seen.

If you think about how trivial these are to bypass, but also that often aligns to fixing the problem for why they're blocked. Iirc port 10443 was abused by malicious actors when home routers accepted Nat- pnp from say an unpatched qnap. Automatically forwarding inbound traffic on 10443 to the nas which has terrible security flaws and was part of a wide spread botnet. If you changed the Web port, you probably also are maintaining the qnap maybe. Also port 25 can be bypassed by using start-tls authenticated mail on 587 or 465 and therefore aren't relaying outbound mail spam from infected local computers.

Overall fair enough.

I did try a custom DNS in the Prowlarr compose stack in Portainer but it didn't help unfortunately. Do you do it a different way?