"In principle, there’s no reason that a certificate couldn’t be issued for an IP address rather than a domain name, and in fact the technical and policy standards for certificates have always allowed this, with a handful of certificate authorities offering this service on a small scale."
LetEncrypt are trialling ip address https/TLS certificates right now:
https://letsencrypt.org/2025/07/01/issuing-our-first-ip-addr...
They say:
"In principle, there’s no reason that a certificate couldn’t be issued for an IP address rather than a domain name, and in fact the technical and policy standards for certificates have always allowed this, with a handful of certificate authorities offering this service on a small scale."