hannes Graphene lacks behind, such as performance
from the website:
[Exec spawning] improves privacy and security at the expense of higher cold start app spawning time and higher initial memory usage. It doesn't impact runtime performance beyond the initial spawning time.
This is the only "performance" thing I could think of. I use quotes around performance because the phone is still performing well, but I don't think this part matters anymore because it's not noticeable on newer phones.
Not about compatibility, but could be viewed as such by some people. On Stock or other versions of Android without secure exec spawning, some apps run fine, but when on GOS they crash, which is usually because those apps have some (hopefully unknown to devs) memory issues.
Other compatibility issues I can think of are: apps that are on Stock but need system access to run (i.e. Android Auto), apps that need to pass Google's crappy safety checks (i.e. Google Wallet's NFC), certain carrier features require proprietary apps/code from Google or carriers to work.
hannes I'm an avid Linux user, so if need be I'm not afraid to tinker around with my devices.
I think one of the best things about GrapheneOS, and why so many people use it, is that it works well without needing to tinker with it. So, if you were accepting advice on this, I'd say since you have a Linux machine and an interest in GrapheneOS maybe you could clone the source code from GrapheneOS's Github and tinker there and leave your phone as is. Maybe over time you could contribute some code to the project.