Shimmering was introduced with SU5 and they don’t care enough to focus on fixing it apparently. Which is a real shame as it’s more or less game breaking.
Join us in the official shimmer bug thread and help keep it alive, share your experiences so maybe it will be fixed one day: https://forums.flightsimulator.com/t/bug-logged-shimmering-aa-downgrade-since-su5-in-game-not-menus-overlays