Yup, I'd say that means @letsencrypt works fine for pure-IPv6 hosts :
2600:3000:2710:200::83 - - [01/Jan/2024:16:16:37 +0000] "GET /.well-known/acme-challenge/y0GGAeXQve8QXRXBFq8crrwnz0pohggiqOe247ilswQ HTTP/1.1" 200 87 "-" "Mozilla/5.0 (compatible; Let's Encrypt validation server; +https://www.letsencrypt.org)"
still can't get Qualys SSL Labs to connect though, and my local mobile network isn't IPv6 enabled to double check
