I noticed that a new free certificate project called ZeroSSL has started working:
ZeroSSL was one of the sites that can issue Let’s Encrypt on the web,
Recently became my own CA. Highly certified by Sectigo.
Caddy is displayed in the list of ACME Automation on this page:
Perhaps we haven’t got a way to issue ZeroSSL with Caddy yet,
but that will be revealed later by ZeroSSL.
Perhaps we could consider adding related Caddy features.