I posted the same problem in a new post yesterday (sorry for that !).
Geo and DaveR helped me to solve this.
I had the problem with “Soften Edges”, but also with shadows, infos, …
Effectively, I was in a very high resolution, with a scaling of 250% ! (which worked perfectly in Sketchup 2019, and no more in 2020 !!!)
The resolution of the problem appeared with a screen resolution of 1920 x 1080, and a scaling of 100%.
With anything higher than this, the problem was still there !
Hope it will help !