Square pixels appear when using brush tool

Does turning off »Use Graphics Processor« in the Performance Preferences (Photoshop > Preferences > Performance > Graphic Processor Settings) and restarting Photoshop have any bearing on the issue? 

Please read this (in particular the section titled "Supply pertinent information for more timely and effective answers”):
https://community.adobe.com/t5/using-the-community/community-how-to-guide-tips-amp-best-practices/td-p/11601738?page=1

@Gurpiar38465804ce8o can you post your Photoshop system info, in Photoshop go to Help > System Info, hit the copy button and paste the entire thing into this thread

in the future, to find the best place to post your message, use the list here, https://community.adobe.com/

p.s. i don't think the adobe website, and forums in particular, are easy to navigate, so don't spend a lot of time searching that forum list. do your best and we'll move the post (like this one has already been moved) if it helps you get responses.

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