[tialaramex]

Although "TLS can be used for those non-HTTP protocols" the tls-alpn-01 validation can only be used on the authorised ports, which for Let's Encrypt is port 443, aka HTTPS.

Now, Let's Encrypt would technically be allowed to enable this validation on a few other ports, 80 (HTTP), 25 (SMTP) and 22 (SSH) under current Baseline Requirements, but understandably they have no plan to do that.

If you actually want certificate issuance unrelated to web servers you should either hook up a web server explicitly for issuance or use DNS proof of control.