nothing happens when I click on quicktime

Launching the QuickTime Player application will start with the default action: an Open dialog box, for selecting a media file to play. Depending on settings, and last use, that may point to the iCloud Drive space, which will not have any compatible files there unless you placed any there.

• Click Cancel to close the Open dialog box. Then explore the menu bar options for what you intend to do.

or

• Select a different side bar location in the Open dialog box, or use the Search box, to find media files on your Mac.

or

• Don’t use the Open dialog box, and open QuickTime Player by double-clicking a media file (.mov, .mp4, etc.) in the Finder.