And they offer a similar service on their DNS resolver over IPv6.
This page lists the IPv6 addresses to use when connecting to their resolver over IPv6
https://developers.cloudflare.com/1.1.1.1/ip-addresses/
and with that I just tried
dig @2606:4700:4700::1111 ch txt whoami.cloudflare +short
And they offer a similar service on their DNS resolver over IPv6.
This page lists the IPv6 addresses to use when connecting to their resolver over IPv6
https://developers.cloudflare.com/1.1.1.1/ip-addresses/
and with that I just tried
And it works, returning the IPv6 address that the request came from :)