reduced FPS when windows placed behind maximized window

First off, I found this while testing a GTK4 port of GtkSourceView and testing performance on HiDPI.

I notice that the FPS of GTK can drop with a maximized window depending on if there are windows beneath the foreground window. Normally, I would expect this case when shadows are being drawn (since it has to expose the windows behind the foreground). But when the window is maximized, all other draws should be able to be culled.

When I move the maximized window to an empty workspace, the framerate increases.

My expectation would be for these to have the same performance since the other windows are fully obscured.