Tailscale makes outbound connections so it circumvents the need for IPv6 with things like CGNAT.
OP, why not use an open source equivalent to Tailscale Funnel? For example, I work on the OpenZiti project and we created zrok.io which is fully open source alternative - https://github.com/openziti/zrok.
I don't use IPv6, so this hasn't been an issue for me. It sounds like a relatively simple thing to fix, though.