My browser / operating system: Windows NT 10.0, Firefox 72.0, Flash 32.0 (release 0)
Occurs over all browsers. No changes to project code, Windows, or browsers were made in between the times the project worked and didn't work.
https://scratch.mit.edu/projects/354082644/ is the affected project.

The Scratch Team has recently released an update to Scratch that change the way mouse-clicks are registered, therefore breaking the ability to use the search bar and close apps in the project above. If this change could be explained, it would be greatly appreciated.

A fix should be coming out (hopefully) soon.

This should now be fixed.

Wow, this is the first time a developer has responded to one of my bug reports AND fixed it. Thank you!