How did you figure that out?
Further suspicion: Apps remain killed, for long periods of time, if I don't start any of them.
Quick test: Kill all apps. Start them one by one. Check if other apps are now running.
Confirmation: Pull APKs from device; RE their code for IPC.
You’ve given me something to think about. Luckily, I only have to amend my mental model a bit, to assume giving a permission to any vendor’s app is to give that permission to every app from that vendor. In most cases where that would be a problem, I already run such apps under a separate user profile, which fully prevents IPC.