I know I'm a bit late to this party, but CGNAT shouldn't be the cause for not being able to connect to games hosted by other players. Being behind CGNAT is a cause for not being able to host games, but connecting to existing games should work with CGNAT as well.
@Vantha I understand that getting your ISP to switch you from CGNAT to a public IP address solved the issue for you, but I guess there was more to it than just this change. My guess is that your ISP does something like filtering traffic for CGNAT users (for example blocking UDP traffic from "unknown" ports), which isn't there for users without CGNAT.