With SQL Developer 19.4 i'm still receiving the error message "No more authentication methods available" while connecting via SSH tunnel. The information in Doc ID 2575854.1 is inadequate, it just points out to regenerate the keys in OpenSSH format.
In my case I've already used keys in OpenSSH format and beginning with 19.2 the connections started to fail. I regenerated the private public keys by using "ssh-keygen" on different platforms (MacOS, Linux) and protocols (RSA 2048, RSA 4096). I also converted the key to RFC4716 format (see https://carsandcode.com/2019/11/21/solved-sql-developer-19-2-no-more-authentication-methods-available-when-using-ssh-connections/). All formats are no longer accepted. In 19.1 the SSH tunnel works fine for me.
What has been changed in SQL Developer? Any clarifications about the OpenSSH format to be used?