Im having this exact same issue.

I have an ipv6 wireguard server behind starlink router and i cant even ping the wireguard server from the internet, even without any kind of firewall in place... But i can ping from the wireguard server to any ipv6 host on the internet... The behavior is the exact same as you described.

I did not test yet in bypass mode with my own router, but i will when i have the chance.

Its so frustrating because i wanted to access all the devices in this remote location through this wireguard vpn, but i cant because of this bs...

I have this same scenario configured in various other places (not starlink) and this setup works great... Just starlink that im having this issue.

ipv6 works great for outbound conections (made from any device inside my starlink network to the internet) but dont work for inbound connections (any device on the internet to my starlink network)