Hmmmm yeah its not showing for me either when I do that. I am not sure why I did not have that issue when I migrated my older files to new version a hwile ago (as they all show the diff toggle). But ok….very odd for sure. Hoping someone on the team will be able to take a look at this to give you a solid answer / solution.
In the meantime, have you tried just starting a new project and either importing it from a zipped file or importing via github connection. I would be curious if that works for you. Can you try one of those methods?
What other UI issues were you facing?