Carrier-grade NAT. Generally rolled out due to IPv4 exhaustion.
Under CGNAT Your router does not get an externally reachable IP address from your ISP, as it sits behind ISP-level NAT router that assigns addresses to subscribers much like your home router assigns addresses to your home machines.
So you can’t run any sort of externally reachable service at all.
Like... what ISP would go out of their way to do that? Call me cynical, but I doubt there's an ISP that uses CGNAT who would forward a port to you. Like, they all do the total absolute minimum necessary to get you Internet access. Why would they bother creating some way to let you forward a port to your computer? No average person needs to do that anymore now that everything is cloud-based. I could be way wrong on this, but I just have my doubts...
Under CGNAT Your router does not get an externally reachable IP address from your ISP, as it sits behind ISP-level NAT router that assigns addresses to subscribers much like your home router assigns addresses to your home machines.
So you can’t run any sort of externally reachable service at all.