>>> THE TRASH WON’T EMPTY

As files you drag to the Trash aren’t immediately deleted, macOS will let you ‘trash’ files that are in use by apps. But when you try to empty the Trash, the system will refuse (pardon the pun), instead saying the item is in use. If you can guess which app was using the file, quit it.

Still won’t empty? Try holding down Opt while doing it. Restarting your Mac may also help. If it still won’t go, try empting the Trash in safe mode. If the Trash won’t empty because an item is ‘locked’, open the Trash, select the item, press Ctrl+I, uncheck where it says Locked and retry.