FYI - UIDesignRequiresCompatibility does not appear in the documentation included with Xcode 26.

I have a macOS 15.0.1 VM and I did not need to take the steps I described. It "just worked". In fact, the Settings app in the macOS 15 VM doesn't show a Mouse or Trackpad entry. Simply configuring the Virtualized Pointer to "Mac Trackpad (macOS 13+)" allows it to work in the VM just as it does on the host. But the macOS 26 VM requires the extra steps for some reason. I don't know if it's a macOS 26 issue or UTM needs an update to support macOS 26 a bit better.

It's a shame the developer forum doesn't put a big banner at the top of the screen for posting a new message about how this is not the place to post bug reports and to use Feedback Assistant, blah blah blah.

I agree. It needs to be fixed sooner than later. My response is a bit fueled with frustration with Apple at the moment. :)