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It's nice to be able to toggle it (it's also possible to revoke this permission on GrapheneOS). However, it is imperfect, since apps within the same profile can still communicate through IPC, so if apps cooperate, network access can still be achieved. I would guess that Play Services is one of the larger offenders, since many apps communicate with Play Services and as far as I understand (but I may be mistaken) Play…
GrapheneOS has user profiles, but they're too heavyweight for most uses.
If you want something less disruptive for isolation, there's Private Space. What I like is that this can stop apps there from working in the background on stock Android as well.