I have had the same issue and thanks to your post I found that any not bordered, and not automatic or default, buttonStyle works correctly (that are: plain and borderless). Moreover the issue is absent on macOS.

Would you provide a sample code?

As today works only with navigationViewStyle using column, or automatic, on iPad started in landscape, I filed a Feedback in Feedback Assistant with a sample project.

Ok. Quit/re open Xcode shouldn't be necessary; perhaps a deeper analysis by Apple with a Feedback Assistant could help. If developer option lastly appears after running an app from Xcode, please set above as valid answer for who will read.

Developer option are activated running an App from Xcode and disappears turning off the iPhone. Are you in this situation?