I believe I found a bug. I have turned off the "standby" norification in recorder settings and it correctly disappeared. However, when I restart the phone, the notification is back. If I open it (and Boldbeast recorder is opened), it disappears.
The standby notification should never appear as it is turned off in settings.
Upon power on the recorder is started, it sits in the background waiting for phone calls to come.
Even if you disabled the notifications, Android 8.0 up still force to display at least once the notification - Google thinks it's important to "make sure the user knows the app is sitting in the background".
This is not a bug, instead it's a standard behavior of Android 8.0 and newer versions. All third-party apps are the same. No one can change the behavior.
But the notification disappears when I open Boldbeast recorder and exit right away. Is it then not important to keep the user notified that the app is still running? Why is there even the option to hide the notification? Btw. I like my notifications always clear, I don't want it there :)
Honesty I can't answer your question.
Only Google can answer your question "why did Google force the system to display the notification at least once?"