Documentation on Local Storage states the following:
identifier is the name of the physical file (with or without full path) containing the database
This is a lie. QQmlLocalStorage::openDatabaseSync method ALWAYS calls QQmlEngine::offlineStorageDatabaseFilePath which ALWAYS prepends QQmlEnginePrivate::offlineStorageDatabaseDirectory to the MD5 hash of the so called "file name". Which means identifier is as far from actual full path as it could possibly be.
Very sad that documentation is misleading, and I had to spend time browsing Qt source code to find out the reason why database with reported file:///C:/Users/ratijas/Documents/MyApp.db URL isn't shared between two apps from the same workspace.
Also, very bad that absolute and relative paths or URLs are not supported.