Thanks for the tips John, I went with these settings. I think a key setting is the minimal quality or whichever setting does not include random buildings as these stop FG starting. I'm not sure if the latest studio or games driver made a difference.
--graphics-preset=minimal-quality
--prop:/sim/rendering/photoscenery/enabled=true
--prop:/sim/rendering/multi-samples=4
--compositor=Compositor/HDR/hdr
I'm really impressed with cloud and landmass reflections - it makes a big difference to the sense of immersion. Compliments to the developers
Landmass reflections sometimes took a while to render more smoothly but they are there (only on the distant shoreline in this picture)
I did experience black blocks over certain parts of the screen frequently that looked like a graphics thing, leaving the sim for a few minutes sometimes cleared the blocks, or changing the size of the screen or rotating the view. I'm not certain but might have been linked to time and recalculating the lighting in the scene/graphics memory - I'm just guessing.