Dependig on the format of the Git repository URL, pipeline creation works or not. I could only get it to work when the format is strict ssh://user@server/repo.git. Anything else led to an error or other weird behaviour, like prompting for username/password to create credentials.
It also wants to either create new credentials or provide a new SSH key to add to the repository instead of prompting for predefined credentials.
None of these happen when I create a Multibranch pipeline job manually.