Google has its own way of telling OEMs which features coming with a new Android build they have to mandatorily offer with their custom skins that rely on the Android Open Source Project, and the ones they can choose to skip. These rules are compiled in the Android Compatibility Definition Document (CDD).
Implementation of new features is divided across categories such as “MUST”, “MUST NOT”, “REQUIRED”, “SHALL”, “SHALL NOT”, “SHOULD”, “SHOULD NOT”, “MAY”, “RECOMMENDED”, and “OPTIONAL.” Now, Google has not released the Android 11 CDD, but a leaked pre-release copy suggests Android 11’s Device Controls in power menu, notification conversations, and on-device identity credentials might not come to all devices.
Google has removed the “MUST” requirement for the new Device Control interface in the power menu, which means OEMs can choose to ignore it and ship their Android 11-based skins without this feature. Similarly, Google is also leaving it up to OEMs if they want to offer notification conversations (group notifications from messaging apps and show them separately in the notifications shade) and Identity Credentials (allows users to securely store identity documents such as driver’s license on their phone) with their respective Android 11 updates.