Sorry to hear about the trouble you are facing. I notice you have modified/created a custom workspace. In that case, sometimes panels get stuck. Try selecting the color guide, brushes, gradients panel, graphic styles, or Align panel and see if you are able to shorten the panel or not.
If that doesn't help, I would suggest you try to reset to default Workspace from the WIndows menu > Workspace > Reset Workspace.
If that doesn't help either, you may try resetting Illustrator Preferences (https://helpx.adobe.com/illustrator/using/setting-preferences.html). Disclaimer: Please note that resetting preferences will remove all the custom settings, and Illustrator will launch with default settings. You can also take a backup of the folders in case you want to. Location is mentioned in the article.