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.

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.

Replying to myself, I'm my case the error was because I code signed the executable, duh.

I bumped into this while adding a static Perl into my App. As an FYI it was a sandbox thing "Process is not in an inherited sandbox": Perl worked fine when called from the App but failed when I poked inside from Terminal and tried to run it while debugging. Spent a good amount of time tracking this down while at the same time making it Fat for Apple Silicon. (Aside: any update on when Perl's (et.al.) removal will be official? ) Process: staticPerl5.30.0 [95059] Path: /Users/USER/Library/Developer/Xcode/DerivedData/Edit_Edge_Data-dpmjxqquuuqzhffrqhwzehmoowtv/Build/Products/Debug/Edit Edge Data.app/Contents/Resources/perlembed/bin/staticPerl5.30.0 Identifier: staticPerl5.30.0 Version: ??? Code Type: X86-64 (Native) Parent Process: bash [13513] Responsible: Terminal [68576] User ID: 502 Date/Time: 2021-05-03 13:42:50.546 -0500 OS Version: macOS 11.3 (20E232) Report Version: 12 Bridge OS Version: 5.3 (18P4556) Anonymous UUID: 88313202-BD67-335F-59FE-96C5DE7681E6 Time Awake Since Boot: 410000 seconds System Integrity Protection: enabled Crashed Thread: 0 Dispatch queue: com.apple.main-thread Exception Type: EXC_BAD_INSTRUCTION (SIGILL) Exception Codes: 0x0000000000000001, 0x0000000000000000 Exception Note: EXC_CORPSE_NOTIFY Termination Signal: Illegal instruction: 4 Termination Reason: Namespace SIGNAL, Code 0x4 Terminating Process: exc handler [95059] Application Specific Information: dyld: launch, running initializers /usr/lib/libSystem.B.dylib Process is not in an inherited sandbox. Application Specific Signatures: Process is not in an inherited sandbox.