Blank windows - licensing

Is this a browser thing or Windows thing? Or Sketchup thing?

Can’t be sure. If you are using SketchUp 2018 still, you could go to this folder:

%AppData%\SketchUp\SketchUp 2018\

and delete the WebCache folder, then reopen SketchUp.

Is there a reason you’re using SketchUp 2018? I think that you have a 2019 license you haven’t yet used. You could download 2019 from here, and see if it works better: