you only have one IP. As you rightfully said, reverse proxy does only http(s), port 80/443. this works because of the nature how http requests work. They carry the hostname as part of the protocol (request headers). SSH is a whole other story, since the client does not send the hostname as part of the protocol, only the IP and the port.
What you can do is forward different ports to different machines… 2021 -> server1, 2022 -> server2, etc.
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