See my Feedback FB21094920. In System Settings a Custom Screen Saver no longer displays it's own thumbnail. If a custom Screen Saver has been installed prior to OS 26 then a cached version of the thumbnail is used but a new version is never used, I've tried PNG/TIFF, .icons, .icns and .xcassets.

I would not have noticed this issue in macOS 15 because I was not changing the icon, and it had been previously cached. With Mac OS 26 and the new glass icons I decided to make an icon upgrade to an App and its associated Screen Saver, that’s when I first became aware of the issue. So I suppose I’m reporting a regression, or simply “hey it’s broke, I want some glass”. The Screen Saver docs do not mention the System Setting thumbnail, but it seems I learned to include two thumbnail files: thumbnail.png 90x58 px thumbnail@2x.png 180x116 px The saver installer then takes these two files and creates thumbnail.tiff, a single file that includes these two PNGs (never knew that was possible!). When I modified the two PNGs there was no change in appearance in the System Settings thumbnail. So the installer was using a cached thumbnail, but I haven’t located where it is. For the test saver in FB21094920 I was never able to set its icon/thumbnail, and it used the blue swirl (I assume) because nothing had ever been cached under that Saver’s name. Thanks for your attention.

At least Mac Catalyst app dev still works. I did essentially all you did except probing https://ppq.apple.com. How did you know about that?

You remembered. As did I, so recently I read your article "Bug Reporting: How and Why?". I'll workup an ER; now that I think about it an extension would simplify things for all. I'll mention the icon/thumbnail.tiff issue too, I made some progress there. Thanks.

Perhaps ending with that question was a mistake; obviously, I should use a new control. But I have used the zoom/no zoom feature since the birth of MacCat in 2019, ... There are two UISceneWindowDelegate methods didUpdateCoordinateSpace and didUpdateEffectiveGeometry, and by inspection it's possible to infer which of the two states the App should configure itself. The problem is that these methods are both “did” variants, there are no “will” methods. My App should never be in fullscreen. (Note Xcode 26.4.1 is aware of willUpdateEffectiveGeometry, but it was never called - maybe in the future.) The new zoom button control worked fine, by setting the scene’s size restriction minimumSize and maximumSize attributes appropriately. Positioning the new zoom control precisely over the green button didn’t work, the green guy intercepted events. Hovering over the green button posts a dialog showing all 15 possible action variations, none useful to me. But, of course, I had long ago missed windowScene.sizeRestrictions.allowsFullScreen = NO. With fullscreen disabled the overlay-zoom-button-over-green-button kludge worked, and the zoom button rapidly became small, round and green.