SFTP with Keyfile and Password

I try to connect to my Server with a Keyfile and a Password, but I can not connect. DO is not asking for the Password and I always get a Message "Server refused our Key" / "No supported authentication methods available". I'm normaly using MobaXterm with this Keyfile and it is working fine. I also checked for the Version of the PPK File. It's Version 2.
What could it be ??

Some older threads likely about the same issue can be found here: