Is your ISP doing CGNAT? At least in the US that's not the norm. Most people have publicly routable IPv4 addresses (even if they rotate somewhat frequently) and most routers are configured to support UPnP out of the box.

This is an example of everything working as intended. The cameras are supposed to be accessable when you're not at home. Of course the cameras ought to ship with randomized default auth on a sticker attached to the unit the same way any half decent router does these days but they don't.