I had the exact same problem and the solution was to ask my ISP who then either just gave me a public IP (Vodafone) or asked for money so my network could be reached from the outside (Primerocom). So check whether there is an option with you ISP to get a “public” IP.

I did my part 😇

@echo_pbreyer@digitalcourage.social MEP for @piratenpartei@piratenpartei.social and the European Pirate Party: https://digitalcourage.social/@echo_pbreyer/112636245969803768