If we have an animation of backdrop-filter, that needs to force the GraphicsLayer structure of a backdropLayer.
<rdar://problem/21082579>
Without this, the element must have an existing backdrop filter or the animation does not work.
<rdar://problem/21082596>
Created attachment 407033 [details] test
Created attachment 466306 [details] Test
The test case I created indicates that this works fine in Safari 16.