Dual-Platform Writing App Development

I’m working on a mobile writing and storytelling community app, similar in spirit to Wattpad. The goal is to release it simultaneously on iOS and Android.

Important note:
The UI/UX is fully designed and written in Arabic, and already completed in Figma.
No UI/UX design work is required — only development and implementation.

Project Requirements

A modern cross-platform framework
(Flutter, React Native, or Kotlin Multiplatform — stability and smooth delivery to both stores is the priority).

Simple and intuitive user authentication (sign up / login).

User profiles.

Story creation and chapter publishing.

A mobile-friendly chapter editor with basic text formatting.

Clean and comfortable reader mode with Dark / Light themes.

Likes and comments system.

Reading progress tracking and sync across devices.

Cloud-based backend (Firebase, Supabase, or another proven and scalable solution).

Project structure that allows future scalability (in-app purchases, subscriptions, memberships).

Deliverables

Full source code with clear build instructions for both iOS and Android.

One working release build for each platform:

iOS (TestFlight ready)

Android (Closed testing on Google Play)

A brief technical hand-off document covering:

App architecture

Key libraries and services

How to push future updates and extend the app in the future

Questions

Which framework do you recommend and why?

Estimated timeline to deliver an MVP that covers the core features above?

Do you have previous experience shipping apps related to:

Writing / note-taking

Community platforms

User-generated content?