Let me state, at the outset, that this is a minor annoyance I can live with. But dang, I am curious what is going on.
I just upgraded to Ubuntu 20.04, Maté DE. Right away, I noticed an aberration when scrolling in three browsers. It looks like a W-shaped distortion in the screen that disappears when I stop scrolling. It is most pronounced in Chrome, a bit thinner in Brave, and very thin in Firefox. No problem scrolling in LibreOffice or Kate, and this did not occur in Mint 19.3 or Ubuntu Maté 18.04
I once read that this is attributable to Window Managers, so I went to Maté Tweaks, Windows, Window Manager. None is selected currently, and the pulldown indicates two Marco options, no compositor and Adaptive Compositor. Would selecting either of these correct the distortion?