⏰ In A Nutshell
Please check the volume you set when saving the alarm, and if "Gradually Increase Volume" feature is enabled.
⏰ To Elaborate
The alarm volume is automatically adjusted to the degree you set when saving the alarm.
Many users use their device on low volume, so the alarm volume should automatically be adjusted as you want regardless of your device volume. Thus, you can change your device volume freely when you are using other apps.
Don't forget to set the volume as you want when setting the alarm!
⏰ Keep This In Mind
Please be aware that if you use "Gradually Increase Volume" feature, the volume starts off very weak. It will increases until it reaches the volume you've set.