Here comes the obligatory warning that opening ports without fully understanding possible consequences is a big risk:
If you make a mistake, or the developer of whatever service you expose to the outside made one that can be exploited and used a stepping stone to attack other things on your internal network, you will not have a good time.
As to your issue, have you verified whether or not your ISP has put you behind a CGNAT? Something like tailscale can help mitigate that.