This weird flickering appears whenever I start playing any game through the Roblox app installed on my Pixel Slate through the Play Store. (Core m3)
I noticed that the flickering will stop while the Chrome OS interface is active, as shown in the video below.
My Slate is currently on Chrome OS 78 (Beta), but this was also happening on the Stable channel (Chrome OS 77) as well.
I don’t know if this is a Chrome OS related problem as it’s not happening on my OnePlus 7 Pro, which is running Android Pie right now.