remote server ssh from MacOS

Either regenerate your ssh-keygen pairs using -t ed25519 and redistribute your keys, or add the following to your $HOME/.ssh/config file:

Host *
    HostkeyAlgorithms        +ssh-rsa
    PubkeyAcceptedAlgorithms +ssh-rsa

The most likely cause is an older set of security protocols and/or key pair. More recent versions of macOS will not use older protocols. You can either modify your client ssh config to accept the old protocols or update the server to use only the newer ones.

On you local system where you are actually typing the ssh command.

Ventura downgraded rsa keys, but if you have been using ssh-keygen generated rsa keys and have distributed them to remote systems, you can still use them, but you need to tell the ssh command it is OK to use them. That is what the +ssh-rsa option is doing.

The alternative is to replace all your rsa keys with ed25519 ssh-keygen created keys, and distribute them to all the remote systems you are going to be logging into using password-less logins.

This has hit the users in the company I work for big-time, so lots of users have been scrambling to figure out how to login to development, test, git, customer, etc... systems. Since Ventura was a permitted upgrade in my company, there are several users per day posting on Slack about not being able to ssh into their remote systems (mostly remote Linux systems).