Hey, I totally understand your concern. Everyone is going through this. For the dates, I recently read here as well : https://www.androidcentral.com/what-scoped-storage . if gets postponed, Android may update. But for now, this is what it is.

So with Google Play updates mail I got this : By August 3, 2020, new apps must target at least Android 10 (API level 29). By November 2, 2020, all apps that are being updated must target at least Android 10 (API level 29) . So I think we may have time. So You can check this. With Android 10, you have got some liberty for now.

To answer the other query:

requestLegacyExternalStorage flag allows apps to temporarily opt out of the changes associated with scoped storage, such as granting access to different directories and different types of media files but till Android 10. This won't work for Android 11. We have to have Scoped Storage.

preserveLegacyExternalStorage flag allows an app to retain legacy storage access on upgrades even while targeting Android 11(recommended way to migrate data that we currently store outside of Scoped Storage).