Please backup your current catalog following the steps mentioned in How to back up catalogs in Lightroom and then reset preferences. Have a look at this article https://www.lightroomqueen.com/articles-page/how-do-i-reset-lightrooms-preferences/ for step by step instructions on restoring preferences.
Note: - Just to ensure you are always clicking/dragging the photo you are trying to move. If you try to drag and drop by clicking on the area surrounding the image it doesn't work.
Hope that helps.
Did you try creating a new collection?
Where is your catalog located?
I tried creating a new collection and even a new catalog, but still could not drag and drop to a collection or within. I just fixed it. I shut down and restarted the Mac computer. I am sure I tired that before, but this time it all seems to be working after the shut down. I don't shut it down often:)