I can indeed curl some other random sites, and - 4 or -6 don’t seem to change much when I try
curl -6 https://acme-v01.api.letsencrypt.org/directory
curl: (7) Couldn’t connect to server
curl https://acme-v01.api.letsencrypt.org/directory
curl: (7) Failed to connect to acme-v01.api.letsencrypt.org port 443: Connection refused
It seems to just fail on acme-v01.api.letsencrypt.org