Abnormal behavior: can't click part of screen

Just upgraded to Big Sur.

2016 MacBook Pro 15"

Regardless of application, there is a zone, in the upper left part of the screen where I can move the mouse, but clicking (either by trackpad or external mouse) does not work. As an example, if a google search in Safari/Chrome/etc. any links in the upper left corner of the page will not work. I can hover and click menus, but not the page unless it is outside of this zone. Excel is the same. I can access and click menus, but the first few rows and columns do not accept a click. Rows and columns outside of the upper left area are clickable. If I scroll or move to a different area of the spreadsheet, then the same area of the screen with new rows and columns will not accept a click. Moving application to a second screen alleviates the problem as well as going full screen with the offending apps. The problem of clicking in the 'dead zone' is alleviated.

What might be causing this problem and how do I remedy it?