sir_brickalot I’m just interested in understanding how the development process usually works and whether new features tend to be added over time to achieve feature parity in GOS or if there is no such thing as feature parity.
The project is heavily focused on security and privacy. The staffing is very small compared to the staffing of Google's OS. I don't believe "feature parity" is a plausible goal for the foreseeable future. In the other direction, GrapheneOS is often ahead of Google when it comes to security and privacy.
sir_brickalot If not, is there a way to know what features will not be available in GOS.
So far the GrapheneOS project does not publish a "roadmap", meaning a list of features and projected dates. As Probably9857 indicated, features that Google donates to AOSP tend to be shipped in GrapheneOS. Note that AOSP has many fewer features than the OS that Google ships on Pixels.
It is likely that many features of Google's OS (or Samsung's OS, etc.) -- especially features unrelated to security and privacy -- will not show up in GrapheneOS for a very long time.