(If anyone at Apple happens to be reading this, I've attached a demo project to FB9575496 demonstrating the issue).

Spent some more time digging - I went as far as disassembling UIKitCore to see what changed. While debugging I noticed some slight differences to a UIScrollView private method between iOS 14/15 (_findScrollableAncestorIfNeededWithEvent:). By subclassing a scroll/collection view and overriding + returning nil from _parentScrollView, you can get the iOS 15 logic to more closely follow what iOS 14 does. This fixes the modal drag issue, but it's not exactly a great workaround... pretty sure Apple won't want us overriding this private API (who knows what other effect it might have).

I've noticed that even after quitting Xcode 13 and simulators, the battery drain is still there (M1 Max 2021). I'm not just closing windows - I'm quitting the applications completely. It's most noticeable while my MacBook sleeps: the battery consistently loses 2% or so per hour. Not a big deal for a couple of hours, but if I leave my MacBook sleeping for 2 or 3 days, I come back to find the battery almost dead. This is very consistently reproducible. If I open Activity Monitor, the '12 hr battery drain' records show that Xcode was indeed the main culprit, despite the fact it was no longer running. Also reproducible: if I cold start my MacBook, and don't open Xcode, sleeping will drain almost no battery, even over longer timespans. Although it might seem odd that the battery drain persists after quitting, it's pretty clearly Xcode that is at fault.

The below provides a quick and simple solution: private struct _ShowsWidgetContainerBackground: EnvironmentKey { static let defaultValue: Bool = true } extension EnvironmentValues { var showsWidgetContainerBackgroundWithFallback: Bool { get { if #available(iOSApplicationExtension 17.0, *) { self.showsWidgetContainerBackground } else { self[_ShowsWidgetContainerBackground.self] } } set {} } } You can use the new environment key showsWidgetContainerBackgroundWithFallback in place of showsWidgetContainerBackground.