Ever since we removed the options to read SSH private keys from the master filesystem, the UI for the 'SSH username with private key' credential type has had only one remaining radio button choice: 'Enter directly.' But this choice is not selected by default, and you can save a useless credential without selecting it. I've been doing remote technical interviews where one of the steps along the way is to create this credential, and as of today ten out of ten candidates have been baffled by this UI, even when they have used Jenkins before. I almost always have to walk them through this part. I think that 'Enter directly' should just be selected by default when the credential is created, and you should not be able to save this credential type if you haven't entered a key. If there is agreement that this would be useful, I can try to create a PR.