Thanks for your constructive suggestions!
I opened a ticket and I will look through them in detail.
https://github.com/aronmolnar/smartphone-hardening-guide/iss...
My problem with GrapheneOS is that only Pixel devices are officially supported, which makes it a very tight use case in my point of view. > "GrapheneOS also supports generic targets, but these aren't suitable for production usage and are only intended for development and testing use."