The latest working public Teredo relay (the one which relays traffic to any IPv6-enabled host from Teredo address), TREX.fi, doesn’t seem to provide Teredo service anymore.
The teredo.trex.fi
address does not ping, does not reply to Teredo packets.
There used to be teredo.remlab.net
from miredo software author, but it stopped its operation in 2021 and domain has been rerouted to TREX IP address. Now it does not resolve at all, after I emailed the author with the news.
The only still working Teredo server known to me is Microsoft’s win10.ipv6.microsoft.com
and win1910.ipv6.microsoft.com
(resolves to different IPs), but it does not provide the relay, and thus does not allow to access IPv6 services over it. It is basically provided for for NAT punching in Xbox games and connectivity inside Teredo network.