From the bug report:

> It turns out Electron was overriding a private AppKit API (_cornerMask) to apply custom corner masks to vibrant views.

> ...

> By removing the custom _cornerMask override and associated logic, we allow AppKit to handle shadows with its default pipeline. This resolves the GPU spike while retaining shadows as expected.

I'd say that most often usage of private APIs is because:

4. it probably shouldn't be done at all