Your device displays the steps to unpin app when someone tries to get out of the app.
So, it means anyone can unpin it. That's why I’m suggesting you to enable the "Ask for pin (your lock method) before unpinning" option at the beginning of this guide.
When you enabled this option, even though someone unpins the app, they are redirected to the home screen and prompted for the pin or password (whatever your lock security is) to unlock your device.
And, it simply makes that you only can access your device and serves the purpose of Screen pinning;
If you want to utilize this feature completely, then you need to enable that option.
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