You might have noticed that ACR has no longer have option to hide the Notification Icon when you are on Android 8.1 or above.
ACR used to use "IMPORTANCE_MIN" https://developer.android.com/reference/android/app/NotificationManager.html#IMPORTANCE_MIN value to have on going notification without icon.
As per the Android reference link above. Android system shows higher-priority notification about the app running in the background.
So, it is not possible to have the Notification behaviour as previous Android versions.
You can however, slide ACR notification to left or right, go to its settings and change its appearance as you wish. Please note that issue
#607 might apply if you completely hide ACR notification.