Earlier quoted context omitted.
Have you got a link to anything about hiding parallel accounts? I use GrapheneOS, and don't see anything in the UI about it. Am I looking for the wrong thing? From what I can see, it's the same as stock Android's user switching, which has obvious UI elements about switching session. I see hidden profiles is an open issue, here: https://github.com/GrapheneOS/os-issue-tracker/issues/5003
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If you do want a smart phone, but don't want rubbish on it, Graphene is very bare-bones by default. F-Droid and other FOSS-friendly app stores can fill in a lot of gaps, and respect your privacy.
Some apps will simply not run without Play Services, but if you had to use such an app, I believe you could do it in a second profile and have Play Services disabled in your main. Regular apps installed for secondary profiles show as "Not installed for this user" in my main, but Play Services is a bit special.