CPU limited scenario then. the CPU can’t feed enough data to the GPU.
Check processor intensive settings like ‘glass panel refresh rate’ (should be medium or low), traffic density (turn AI / multiplayer off to test).
Heavy photogrammetry areas and large / complex custom airports are CPU hogs as well, especially at large render distances.
If you’ve downloaded loads of custom sceneries (especially google-earth ripped off area mods); those are terrible (not optimized at all). Get rid of those.
Also check that newly installed NVidia drivers / experience haven’t messed with your settings.
Could also be a mod you’ve added maybe.