That was basically it. I changed my size classes from wR/hC (Regular/Compact) to just hC (Any/Compact) and it works as expected.

I think I just discovered the same issue, in the Xcode simulator running iOS 17.4. I am debugging my app in Dark mode, all of my view controllers are set to backgroundColor =.systemBackground, and they all appear dark black except for one view controller with a "push" segue (I've also tried a "modal" segue). That view has what appears to be a very slightly translucent background which appears dark gray not black. Compare to one of my other view controllers that is part of a tab bar set.