Several years ago, if one wanted to setup an appliance (typically a web cam) that could be accessed from the Internet, then port forwarding had to be enabled on the Internet modem. That was always a point of contention for the camera owners since port forwarding was not always easy to setup. I had a couple of old web cams at my cabin that used port forwarding. It was always a problem to trouble-shoot issues to figure out what was broke. If I traded out the Internet modem, I had to setup port forwarding again on the replacement modem. I have since replaced those cameras with P2N devices. Port forwarding was also required if one wanted to access their network from a remote location using RDP.
Today, if you see any appliance that needs port forwarding setup for Internet access, then I would steer clear of using that appliance.
Modern day appliances use P2P for allowing remote Internet access to a device sitting behind a firewall.
https://en.wikipedia.org/wiki/Peer-to-peer
https://www.geeksforgeeks.org/what-is-p2ppeer-to-peer-process/
P2P allows setup of the device in a couple of minutes, without requiring any changes to a firewall.
All P2P implementations are not created equal. Some, such as the Splashtop app are very secure. Others, such as the MontavueGo app are not secure. Montavue is banned from selling any new models of NVRs until the models have received FCC certification.