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.