You can do TURN using TLS/TCP over port 443. This can fool some firewalls, but will still fail for instances when an intercepting HTTP proxy is used.

The neat thing about ICE is that you get automatic fallbacks and best path selection. So best case IPv6 UDP, worst case TCP/TLS

One of the nice things about HTTP3 and QUIC will be that UDP port 443 will be more likely to be open in the future.