The only thing that worked for me was to have QuickBooks desktop open on the main screen of a multi-screen set up.  If you have QuickBooks open on any of the other screens the "resize" "+" symbol doesn't even show up, just the hand symbol that allows you to move the columns.  When you have QuickBooks open on the main screen you can resize at will. 

I have been fighting with this for weeks. 

This is something QuickBooks technical support should address real soon.  It wasn't this way until I installed 2021 QB and updates to all the other versions.  They changed something and they should fix it!!