On Mac if you create a new scene using the Lightweight Render Pipeline template, Scene view will be filled with random garbage pixels unless you ended your previous Editor session with the Default window layout. When the problem occurs you can make it go away for the remainder of your Editor session via Window > Layouts > Default, then repositioning your windows however you like them.

I saw this problem occur using the 2 x 3 layout, and custom layouts derived from the 2 x 3 layout.

This is thought to be specific to Metal on older MacOSX versions (i.e. MacOS 10.11.6). An additional workaround is to disable Metal Editor Support in Player settings then re-start the Unity Editor.