Direct Client Connections (DCC) became infeasible about 20 years ago with the proliferation of NAT routers. The workarounds (connection tracking and rewriting) never arrived for the masses.
Default IPv6 (for consumers) is block all incoming (except for traffic related to outgoing). Then with user authorization add allow rules as needed.
So basically no difference between IPv4 vs IPv6.
If you default firewall on IPv6 is allow all... buy a better router/firewall.