Mouse movement leaving grey pixelated areas around artboards

[e.tumilty1]

I'm working on Adobe Illustrator 2021, on a 2012 Macbook Pro, OS Mojave 10.14.6. 

Since updating to 2021, Illustrator has been very strange. This is one of a number of problems I am having (posting separately). 
When I move the mouse around outside artboards it creates a grey pixelated "brush" for want of a better word - leaving greyed out areas wherever the mouse has moved. 
What is happening here? How do I stop it? It's very distracting and to be frank - this update totally sucks.

[Anubhav M · Accepted solution]

Hello e.tumilty1,

Sorry to hear about this experience. I would request you try resetting Illustrator's preferences by following the steps shared in this article (https://helpx.adobe.com/illustrator/kb/troubleshoot-preference-issues.html) and sharing your observations.
Disclaimer: Please note that resetting preferences will remove all custom settings, and Illustrator will launch with the defaults. You may take a backup of these settings from the location mentioned in the article. 
 

Also, try downgrading to an older version of Illustrator and check if it helps.

Looking forward to hearing from you.

Thanks,
Anubhav