It should also require allowing incoming connections.
Too much ISPs, especially mobile, are gives one-way Internet now. Basically like having a phone line with no phone number.
You should google "CG-NAT" and learn why mobile providers don't (and simply can't) provide you a public IP. Get yourself a cheap VPS, set up a reverse proxy, and open all the ports you want.
IPv6 is actually widely implemented. Home ISPs are mixed on providing IPv6, but mobile providers widely embrace IPv6, some even running IPv6-only networks that rely on translation services to reach IPv4 destinations. T-Mobile is IPv6-only for example