How do I close Preview using the Force Quit window? If either of these methods works, make sure you reboot your Mac before opening Preview again. There are two ways to Force Quit an app in macOS: using the Force Quit window or using Activity Monitor. But it has frozen and needs to be reopened. Despite the error message telling you Preview “is not open anymore,” it usually is. The first thing to try and do - although it doesn’t always work for this error - is to close the unresponsive app.
Can’t delete a file on macOS because it’s ‘In Use’? Try this!.How to quickly restart or relaunch Finder in macOS.