Yes, that’s why you can’t just rely on permissions and have to install trustworthy apps.
You could also take a look at (on Pie) Settings > Security > Trust > Privacy Guard > 3dots > Advanced, in order to be able to choose which apps are allowed to start at boot or run in background (among other things).
And in Developer options (that you have to enable), it’s also interesting to look at “Running services”. Only apps that you are currently using should be running. If you see an app that should be completely closed, then check the Privacy Guard settings of this app as mentioned above to disable its permission to run in background or to start at boot.
I didn’t know Privacy Breacher, which is the perfect example of what I said earlier, thanks.