Thanks, bug. It’s gotten better for those of us with some background, but I’d definitely not say it’s trivial for a regular android user to use. GrapheneOS only supports Google Pixels launched after August 2020 for starters. The recommended to install GrapheneOS still needs you to OEM unlock and may need a factory reset as well. Jailbreaking might technically be harder, but this is hard enough.
The only way something like this can become mainstream is if popular smartphone manufacturers intentionally supported an alternative distribution (like GrapheneOS), which i don’t see happening for business reasons including the possibility of a fallout with Google.
Even though android is open-source, the hurdles for running an alternative are around the proprietary stuff we depend on in the ecosystem.