Why you need this? You can get SSL certificates IP addresses Anything that is 'common name'.
https://1234:5678:9abc:def0:1234:5678:9abc:def0. should work just as well as https://1234-5678-9abc-def0-1234-5678-9abc-def0.has-a.name.
Right?
https://1234:5678:9abc:def0:1234:5678:9abc:def0. should work just as well as https://1234-5678-9abc-def0-1234-5678-9abc-def0.has-a.name.
Right?
Of course, has-a.name will be rate-limited to 50 certificate a week by Letsencrypt until they get themselves onto the public suffix list. And whether it's a good idea to bypass LE's no-certs-for-ip-addresses policy is another matter...
In order for a wildcard to work, every single user of the service needs the private key for that wildcard certificate.
It's your domain, you ought to own it. Obviously no one else should. If you buy a wildcard cert from say Comodo (or a number of other cert houses) you can use that cert on any provider you wish, or use it on your locally own infrastructure. You get the private and public key, as you should.