Simple reason being that there’s no notoriously good OS for Samsung phones.
Graphene is highly focused on not being annoying while keeping privacy intact. You can, for example, have Google Play Services, within a sandbox. Everything can be denied network access, or any access really, on a per app basis.
It also relies on Google’s security chip to keep the chain of trust intact. The boot sequence and your private keys are kept intact that way. Not everyone documents and opens their hardware as well as Google. Samsung is notoriously terrible and full of it when it comes to allowing you to do your own thing.
What is that? Google translate listening and translating live? Google lens translating images? Both work.
No clue about what that is.
In general most things work just the same, and things that do not tend to be listed in the Graphene docs.