Any thoughts/updates on this from an Apple engineer working on Xcode & Icon Composer would be appreciated.

The issue appears to be improved or even entirely resolved by macOS 15.4 Beta 1 based on my own testing in various affected apps (Settings primarily) on my M2 MacBook Air.

The feedback I filed for this issue (which I made sure included a direct link to this thread and it's information) was recently marked as "Potential fix identified - For a future OS update" so hopefully Apple ships said fix in one of the upcoming 15.2 beta builds. FB ID is FB15241636.

Is this, per-chance, the very reason that scrolling is laggy in System Settings, Tips and Notification Centre in macOS Sequoia then? (All seem to be SwiftUI afaik and all of them had buttery smooth scrolling in macOS 14).