Prevent Preview from opening "Open" file explorer when taking screenshot

Solution 1:

As mentioned in the Comments, the behaviour to open screenshots in Preview is set using Command Shift 5. Once set, then all screenshots will be handled this way (including using Command Shift 4).

Preview is set to show an open dialog when it is launched or brought to the foreground and no document window exists.

It would seem to be a bug that the screenshot document is not counted.

If you want to stop the open dialog, then you have to do the following:

Open System Preferences > iCloud > iCloud Drive > Options. Uncheck Preview.

(as per this discussion) https://discussions.apple.com/thread/7936364

Otherwise, you might want to consider not opening all screenshots in Preview, but choosing another behaviour for Screenshots.