Hi Naveen,
OutSystems mobile apps are basically javascript (reactjs framework), css, and html hosted in a webview using Cordova framework. This allows to code once and build it for iOS and Android. Since this year your OutSystems mobile application can also be distributed as a PWA, that is then all I described without the Cordova framework, as a PWA your mobile application is directly run in your device browser.
For more information read this official OutSystems documentation:
https://www.outsystems.com/blog/posts/how-mobile-apps-build-service-works/
Regards,
Daniel