Downloading large files in background on iOS 12 I usually download large file in YouTube app for offline viewing , also use “Shortcut” app to download large file, I have set background refresh on for both the apps

The problem is that , the moment I switch to other app download stops immediately and restarts when I open the app again , this also happens when screen locks automatically.

Is there any way to download file without keeping screen on till the download completes ?
As long as it is not implemented by the developer, there is no way to keep downloading in the background.  

If you are interested you can read up on that in apples developer documentation here