How can I disable "app is running in the background" notifications?
I am on Oreo 8.0.0 and couldn't find a setting for this so ended up using this Hide  "running in the background" Notification

I have several apps running in background and disabled them all using this app, as it serves no useful purpose for me to know

Auto Notification is another app that has this feature amongst other Tasker oriented features if you are interested. 

I preferred the first one since I don't use Tasker

Edit: These are Bye the way notifications