Oh my. I can confirm the bug as well, didn’t notice it since I do not much use the selfie camera.
Fairphone 4, 1.5.1-s stable.
Same error message when I try to open camera ID 3. Weird that this hasn’t be tested though…
Did you try to clear camera app cache and user data?
If still doesn’t work you might search if an issue is already opened on Gitlab, and if not open a new issue.
Edit: Clearing cache and user data does not help.
I moreover noticed that one can still use the selfie camera by using the double arrows icon just to the right of the photo capture button. So in reality all lenses are working well, but the ID:3 camera should be removed from the app to avoid the error message.