@Desbrina did you ever find an answer to this?

In case anyone else has the same issue I had "Full Keyboard Access" enabled. Turning it off fixed the problem.

I am having exactly the same issue on my iPhone se2! It works fine in the simulator but on my device either doesn't switch between tabs at all, or switches once then freezes. I am getting the same "Class CKBrowserSwitcherViewController overrides the -traitCollection getter" error as you. I wasn't sure if the error was just a red herring though as people seem to think similar errors can be safely ignored https://developer.apple.com/forums/thread/118599. Did you manage to find a solution at all? Driving me crazy not being able to test on device.