Sadly, most of the ones I’ve found are too complicated, and getting all devices to accept the CA is more hassle than it’s worth for self hosting. I’ve given up and just buy my wildcard cert for 60$/yr and just put it on everything.

The DNS-01 challenge can be used to generate a wildcard by creating the requested dns record in your public dns zone, then you can use that cert for internal servers/dns. With certain dns providers it can even be automated.

https://eff-certbot.readthedocs.io/en/stable/using.html#third-party-plugins