I try to use Rex 6 with MSFS2020. However there are issues between MSFS2020 and Rex 6 (windows 10 OS)where Rex 6 will not produce correct local weather. I have had far more accurate weather results using MSFS2020 weather. My experience with support from Rexsimulations is poor - and (they don’t refund). I suggest any MSFS2020 who may think about purchasing Rex 6 as an addon for MSFS2020 give it some serious consideration.
I am also finding the way to generate 2 or 3 layers of Clouds (or wind) in REX 6.
Seems now the vanilla MSFS weather is quite significantly rendered.
However, REX is undergoing a back-end server update, so that’s some refresh will be arrive soon -