Not possible without a domain, even just "something.xyz".

The way it works is this:

• Your operating system has some trusted certificate root authorities root certificates installed from installation of the OS. All OS have this, Linux, Windows, iOS, macos, Android, BSD.
• when your browser goes to a Web url and it is a https encrypted site it reads the certificate.
• the certificate has a certificate subject name on it. It also may optionally have some alternative names.
• the browser then checks if the subject name matches the Web url address. If it does, that's check one.
• next it checks the certificate validity: it looks at the certificate chain of trust to see if it was signed by a intermediary and then the intermediary was signed by a root certificate authority. Then it can check if any certificate has been revoked along the way.
• if that's all good, then you'll open without a single warning, and you browse Web sites all day long without any issue.

Now, to get that experience you need to meet those conditions. The machine trying to browse to your website needs to trust the certificate that's presented. So you have a few ways as I previously described.

Note there's no reverse proxy here. But it's also not a toggle on a Web server.

So you don't need a reverse proxy. Reverse proxies allow some cool things but here's two things they solve that you may need solving:

• when you only own one public IP but you have two Web servers (both listening to 443/80), you need something that looks at incoming requests and identifies based on the http request from the client connecting in 'oh you're after website a' and 'you're after website b".
• when you have two Web servers running on a single server, you have to have each Web server listening on different ports so you might choose 444/81 for the second Web server. You don't want to offer those non standard ports to public so instead you route traffic via a reverse proxy inbound and it listens for both Web servers on 80/443 and translates it back to the server.

But in this case you don't really need to if you have lots of ips since you're not offering publicly you're offering over tailscale and both Web servers can be accessed directly.