I had seen that too, and a couple of others reported the issue.
The file where the column widths are stored is in this file (you can use the Go menu in Finder, and choose Go to Folder… then paste in this text):
~/Library/Application Support/SketchUp 2021/SketchUp/
Close SketchUp, go to that folder, and rename the PrivatePreferences.json file to some other name. Reopen SketchUp and the columns should be ok.
You may need to reposition palettes afterwards, and set up shortcut keys again.