In macOS 26 Apple enforced the squircle shape for app icons. If an icon doesn't match the new format, it gets "plated" with a gray background.

I noticed that a few apps that weren't updated for a while had their icons shown without extra plating. This surprised me, since all macOS icons before version 26 are transparent images with graphics and shadows baked in.

It seems macOS 26 automatically detects if old app icon image uses the official icon template and doesn't have any protrusions.