There is no mandate for you to update, only your desire towards new features that iOS 14 may provide specific to your app, and of course any issues that may be new to it when running under iOS 14.
Best to test against it to your users don't have to ;), in which case you'll need Xcode 12.
Apple usually does a good job of not breaking current apps in the store when a major new iOS hits the street, but again, get your testing done so you can proceed accordingly.
Good luck.