Don’t bother with VPN it will only make things more complicated.
UPnP or manual forwarding the server will only try one of the other depending on if the manually specify port is enabled and filled out. for port forwarding (which I recommend) need to enable and fill out that field. for UPnP disable.
Do you have a old router you could switch out see if it’s the router? I had to reboot my eero router when setting port forwarding before it would take. Thus why I switched to an ASUS router lol.