Unity Android game works on new Android versions but not in an old version?

So I finally published my app on the Google Play store. So far I’ve had it work on two modern android phones. But I made my friend try it, who has an old phone that only runs Android 5.1.1. The game wouldn’t even launch on his phone. Yet in the Unity Build Settings “Other Settings”, it says that the minimum API level is Android 4.1, which makes me assume that it should work on Android 5. I have no idea what I could do to get to the bottom of this. What could I possibly do?

Unity has checklist for that https://docs.unity3d.com/Manual/TroubleShootingAndroid.html

Specially the adb logcat is useful for figuring out where the crash actually happens