You’re welcome, great to see how you’re taking all the comments on board!

There are more subtle problems with NAT as well. Say that PC-A opens a connection from port 1234 (to something on the internet), and PC-B opens a connection from port 1234 too. Now the router has to translate the PC-B connection to coming from port 1235 to distinguish them from each other. But if PC-C then wants to open a listening port on 1235 it won’t work because the port is already in use, even though you can’t see anything using that port!

NAT is full of ridiculous corner cases like that, which normal users aren’t very likely to notice. But once you start self-hosting things or trying to get something like older multiplayer games working the problems pile up fast if you’re unlucky.