Check your App license. (iOS Developer Program or iOS Developer Enterprise Program)
But if it's for private use (if you have any iOS Developer license), and the total users is 100< then you could distribute your app just using:
This is a tool for developers who use the hosted builder. With this tool your beta testers can install your app over the air by clicking on a link. In order to distribute your app you need to follow these steps: 1. Add the beta tester device UDID to the provision file and download the updated...
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Manage both your iOS and Android pre-release distributions and get your apps onto testers' devices quickly so you can get feedback early and often.
this way you don't need to public your App on Apple Store
in the other hand, if your App has login then then it's not really important if you public your App on Apple Store, you can control who will have access to your App, but in this case Apple will review your App before publishing it