Need Help! How to create cross-platform compatible WebGL, iPhone and Android app?

I am trying to create an app which might go viral. I have a lot of experience working in Unity for PC development, but I have close to none experience on how to build an app which will be cross-platform compatible.

I tried using URP with 2D new renderer, it worked fine in play mode but it didnt work in WebGL. On high quality, lights were non-existent and on ultra, whole screen was black.

The app is completely 2D, very few sprites with physics system.

The most important thing is that the app should behave same on webgl, iphone and android.

Questions:
-Should I use URP with new 2D renderer, or Built-in pipeline?
-Which version of Unity should I use?
-I read something about webgl 1.x and 2.0 and that isnt supported everywhere
-Any other tips?

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