I think the only reason you need to connect to localhost would be to set up the initial (bootstrap) admin account - see https://www.keycloak.org/server/configuration#_creating_the_initial_admin_user or https://www.keycloak.org/server/bootstrap-admin-recovery.

Regardless, if you need to connect to the server's localhost there are some tricks like setting up a dynamic proxy via SSH (using the -D flag) to forward HTTP connections to the server, delegating DNS resolution to the target server and setting up an entry that resolves to 127.0.0.1 in /etc/hosts, or using a forward TCP proxy via SSH (using the -L flag). Both are explained in a RedHat blog post from 2021 called "How to set up SSH dynamic port forwarding on Linux".