Annoying FPS eating (Cannot develop the game)

Without any further investigation I can safely say that you are getting expected performance as to your settings.
6 shadow cascades, covering 60000 units, coupled with relatively high-poly foliage with no LODs, that was designed primary for ArchViz. You are trying to render above 100 million triangles each frame. That is an order of magnitude above of what you should realistically aim for.