> It means malware can’t exfiltrate the SSH key from your machine and keep using it

Are you sure about that? Presumably the secret parts of the SSH key are being read into memory at some point, or a RCE could dump the key the same way ssh-tpm-agent does.

Don't rely on a TPM to store secrets. Use a secrets store that can be audited for use and have it generate dynamic, short lived credentials. For SSH, use SSH CAs.