jmo DNS filtering is not a fundamental privacy improvement. It's used to block client-side connections to services resolved through the system DNS resolver which are not used to provide useful functionality. It does not work the way you believe it does for multiple reasons.
Anything used to provide useful functionality cannot be blocked without breaking it. Any connection considered to be part of things like tracking still works fine as long as the service also provides useful functionality too.
App developers can and do connect to third parties from their application servers instead of doing it from their app. Doing it from the server is considered to be better in general, since it avoids filtering, avoids leaking API keys and is under the control of their server rather than an app which could be modified.
Aside from those massive limitations, it is based on enumerating badness which is not a working approach to providing fundamentally better privacy and security.
It is a very weak way of eliminating some connections to third parties from apps which they can instead from their servers to avoid any client-side filtering.
GrapheneOS does not include DNS filtering because it can be done via an app while still using a VPN and it doesn't really fit into our approach.
Filtering within a browser has all these limitations too, but DNS filtering is even less capable than doing it within a browser where it can be finer-grained.