Background question. iOS bug?

My team is developing an application for sports. It is essential to be able to have the mobile screen turned off, so the user will continue to listen to audios in a programmed way (and that the mobile vibrates). We have looked at the official documentation, (Background Modes), and it seems that it would only be possible to do something similar through notifications, but in a limited way.

There are other sports applications that stay in the background making sounds and vibrating the phone, but they do not use notifications.

We have not found a solution for days. It only occurs to us that there are bugs in iOS that those applications use to be able to stay in the background for an unlimited time.
Playing audio is one of the few officially supported reasons to keep your app running in the background. Perhaps that’s what they’re using?
The device vibrate too when the mobile screen is turned off. They do not use notifications. Here two examples:

https://apps.apple.com/es/app/hiit-tabata-fitness-app/id1035873240
https://apps.apple.com/es/app/tabata-timer-interval-timer/id1255964203
Background question. iOS bug?
 
 
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