If you really don't care, sometimes you can just go plantext HTTP. I do this for some internal things that are accessed over VPN links. Of course, that only works if you're not doing anything that browsers require HTTPS for.

Alternatively, I would suggest letsencrypt with DNS verification. Little bit of setup work, but low maintenance work and zero effort on clients.

Or just run tailscale and let it take care of the certs for you. I hate to sound like a shill, but damn does it make it easier.