Alarms play at max volume

Most likely, your Backup alarm went off after your regular alarm failed tp wake you up. T Backup alarm is triggered when there is no interaction (no snooze, no dismiss) for more than 20 minutes.

Make sure you are using a loud enough volume in the system settings. If you are using a current system volume, you risk the volume won’t be suitable for you when the alarm starts. Any app can change this volume.

Enable Gentle Volume in Settings → Alarms → Gentle wake up → Gentle volume

Try vibrations (Settings → Alarms → → Gentle wake up → Vibrate).