It needs to be able to render 4k
Starting in version 1.0.2 you can edit and export up to 4k 60p on supported iOS devices (also possible on Rush desktop but that was available in version 1.0).
If you have other specific request relating to 4k please create a new Idea.
Ruben Herrera Jr4K60fps commented
You can edit and export 4k video in Rush today. Is this not working for you? Can you explain your workflow?
It's possible that your project is not 4k, in that case on iOS ONLY, we only support exporting to 1080p. If you have a 1080p project on desktop, we do support exporting to 4k.
Hope that helps!