There are apps installed on the OnePlus smartphone that will sooner or later request permission to appear or show over other apps.
A very fitting example is the Facebook Messenger app, which displays the profile photo of the chat partner at the edge of the screen when a new message is received in a conversation or chat.
- Open the Settings
- Tap on Apps & notifications
- Tap on Special app access
- Tap on Display over other apps
- Choose an app
- Enable or disable Allow display over other apps