That isn't strictly true, several apps have launched their iOS14 ready versions ahead of the public release. All they can't do is use new SDK features.
You say "tightened up" and perhaps that's what they meant internally, but as it stands my (simple) app's behavior when using the search bar is different and broken on the new update even though I'm using the API in a supported way. So it's really a bug.
~All of the bugs I've ever seen on a new iOS release are just where they've tightened up some behaviour.