What you describe implies to me incorrect installation of SketchUp, which, on Windows 10 and 11 requires right clicking on the downloaded installer and selecting Run as administrator. With correct installation you shouldn’t need to do all those gymnastics.
Please complete and update your forum profile. It says you are using Windows 7 and doesn’t identify Sketchup version. If you’ve got a new computer probably a new graphics card, too.
Two or three SketchUp versions have initially been released without thumbnails working but they all have had them fixed in a maintenance release, so all versions of SketchUp ought to display thumbnails without any extra gymnastics if properly installed. Cold reboot your computer after making changes to these things.