I might have a partial solution for some of you:
Had severe graphical glitches in Outlook 365 (App, not Web version) when hovering with the mouse over emails list or moving along title bar / top window border. When hovering emails, the cursor would sometimes jump to non-logical spots (e.g. mouse moved upwards, cursor jumping to an email further down). In the title bar, some parts of the screen would flash UI elements to locations where they don't belong etc.
I analyzed this issue further and found that it has to do with mouse movements. When trying to operate Outlook with the keyboard only, everything was ok. I then checked whether a different mouse driver (Logitech Anywhere 2S in my case, tried out drivers from Logitech vs std Microsoft ones) or a different link to my PC (Bluetooth vs Logi Dongle) might do the trick, to no avail.
I tried 20 different settings in my AMD Adrenaline panel (Radeon 6800XT card) - nothing.
I then tried to play around with ouse settings and ACTIVATED MOUSE CURSOR TRACES in the system panel / mouse settings. BOOM! No more glitches!
It seems that mouse driver, windows redraws and graphics card hardware features (acceleration) are not matching up to each other, but at least this is a quick fix