The choice of technology stack for an online food ordering app depends upon your requirements and the features you want to include in it.
However, here are a few technology stacks mostly used in such applications:
Admin panel and API: React.JS in Frontend and Node.Js in the backend.
Delivery and user app: Java, Kotlin, or Android Studio for Android development, Objective C, Swift, and Xcode for iOS development, and Flutter for cross-platform app development.