While it seems theoretically possible to obtain a certificate for an IP address (though it seems to be a deprecated practice nowadays), it’s unlikely that you really need it…
You need to understand why do certificate exists. Certificates are meant to ensure the authenticity of the server you access. If you access your server via its IP address, then you are probably the admin of the server, or tech-savy enough to check manually that the self-signed certificate shown in your browser corresponds to the one actually on your server, and manually add the exception.
A “regular human being” will access to your server via its domain name, not via its IP.