Oddbean new post about login | logout @final [GrapheneOS] 📱👁️🗨️ what would be needed to make this a reality?
Check the above link, there is a full list of requirements in the FAQ
Someone could build their own OS which can be based on GrapheneOS. It's permissible as long as people don't present it as the genuine GrapheneOS. https://grapheneos.org/build The end result still wouldn't be GrapheneOS though, and the security GrapheneOS has cannot be guaranteed on these builds. Some features are also entirely dependent on the hardware like MTE for newer Pixels or the Tensor Pixels USB-C port controls.
More information on how it would be phrased can be seen here: https://grapheneos.org/faq#trademark