Hello @Pierre92 and welcome to the forum!
Was there ever a username and password, for example from a different storage type that needed those? Changing “Storage Type” sometimes leaves leftovers from the previous type that don’t suit the new type. Clicking “Manually type path” on the Destination screen will show you the storage URL then you can edit.
It sounds like the username and password were only an experiment to understand this problem behavior. Because there have been other reports of “auth-u” (including mine), I also experimented, and because it appeared that the truncated option was consistently a question mark then six characters I suspect a bug:
which starts after the seven characters file:// but goes seven characters too far (if it can) at the ending.