@QuantumByte43 - Boosting this; I agree that neither of those other threads (including mine) have addressed our questions about the nature and timing of the deprecations. In particular, I haven't been able to find any information about the interim non-resizable window behavior.

I'm curious about this as well. We have a CAD-like interface that is very dense and not conducive to multitasking. The documentation for the plist key doesn't mention anything about its deprecation, but it does not prevent windowing in the latest iPadOS beta. The related WWDC video says "Every app that supports multitasking now shows a handle in the bottom right corner." But in reality, it appears that there is no way to opt out of this.

Is standardAppearance deprecated? Why do those APIs have no effect on the new tab bar UI?