Notification until user interaction

I'm developing an application (SwiftUI) that needs an alarm, but from what I've read, it's not possible to do it like the iPhone alarm, nor is there a special permission that can do it, so I imagined doing it by sending incessant notifications until the user interacts with the application, something that I also didn't find because they say there is a limit of 64 notifications, but the "Alarmy" application makes these incessant notifications until the user interacts, but in the forums I read nobody knew how they did it, I imagine it could be remotely, but I tested the application without internet and it worked normally, the application sends 2 notifications every 3 seconds, I tested it for more than 5 minutes, which exceeds the limit of 64, so I ask you, how do you imagine they achieved this? A special permission maybe?

Notification until user interaction
 
 
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