If they’re providing IPv6 to you, port forwarding shouldn’t be necessary most of the time for online gaming.

Are they allowing UPnP upstream?

If you’re getting a /64 from your ISP via DHCPv6, you likely need to send a prefix hint. I’d guess /60. Then you’ll have multiple /64s to work with on your inside interfaces.

Who is the ISP?

If purchasing isn’t ownership, piracy isn’t stealing.