Thinking about putting GrapheneOS on my dads phone

I’d say he’ll notice. Apps can and do introduce stricter verdicts or otherwise break. Sandboxed Play Services, while very stable for what it is, will by definition prompt him considerably more than on stock due to lacking system-level integration. There is some confusing UX behavior from Play seeking to install suite of Google bloatware that needs to be worked around by GOS, as well as the uncertain status of RCS if he ever needs it. My parents are quite tech-literate, but if I switched them to GrapheneOS, I would drown in tech support issues.