How to convert multiple scenes to png
I don’t want to shoot the renderer like above.
Given a scene and camera, I want to output a png with just that.

Is there no way?

you can export the render context to blob and then use JS apis to export the blob to a file. You will need to run the app on a basic localhost server like simple python or node to get async functions to work.
Youll also need to set render settings to double buffer or save buffer instead of clearing
You have to find the actual technical terms, but thats the concept