Slightly tangential, I've tried using various Pomodoro apps on iOS, and none of them seem to be able to alert me when the phone has turned the screen off. Is th

Slightly tangential, I've tried using various Pomodoro apps on iOS, and none of them seem to be able to alert me when the phone has turned the screen off. Is this an iOS restriction? I can imagine that apps are restricted when not in focus, and even more so if the phone is not being used at all. The only app that can raise an alert is the built in iOS timer, which honestly does 95% of the job, so I use that instead.