Fix for this issue is now available in the latest update of InDesign 2021 – that is, InDesign 16.2.1
In the Creative Cloud Desktop application, click on the Updates section on the left. You should be able to see the Update available for InDesign. Please update your InDesign application to this version to try out the fix.
Let us know in the comments section if you still face this problem.
Adobe InDesign Team
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I'm seeing strange red and black lines filling up the page when I have a document open!