Ok I see. I have never worked with Unreal. So I am just guessing judging by what I have read elsewhere.
Let’s just assume that you cannot readily export some things from Unreal (that can be rendered within 60fps). In cases like that you need a workflow to detect incompatible objects. You know like, in Unreal you name the “grass field” object “$Grass” and when you load that object in Babylon, see the name “$Grass”, you know you have to replace it with thin instances and add a shader (or so).
The other challenge can be, depending on how incompaible features are, to replicate that feature in Babylon. This is where you necessrily learn your way through.
Or you know what: Make a quick and dirty level in Unreal with all the features you want (wavy stuff, flowing water, etc.). Then export the level to a glb file. Then drag this file into here: https://sandbox.babylonjs.com/ See what happens.