We got Angular, React, Vue.js. Those typescript UI frameworks can provide a rich user experience to the user in a mobile web interface. Do we need to build Mobile App?
Yes! In some situations, that is the truth. For example, if you do not have any native functions from a mobile phone, such as GPS and notifications, you do not need to build any mobile app. Moreover, you spend the time to publish your app in the app store or play store. The users do not need to download the app. You only need to give the URL to your users.
However, if your app is required to access the native features a lot, such as GPS, camera, and notification, I suggest you build a mobile app. The mobile app is better to handle those functions. If you want to have some background tasks in your app, the native app is better in this area too!
Thus, whether you should build a mobile app, that depends on what you want.