For UE use : do your best to generate decent-ish UVs (ideally by proactively marking seams on the pieces as you model them), and bake down the Blender bevel node (or the Modo/Max/Maya equivalent) to a normalmap. Or, bake everything (with hard edges) as an Object Space normalmap, blur it ever so slightly, and convert it…
You can achieve the look of a high poly model using the rounded edges node inside of Arnold Render. Take a look at the documentation here: https://docs.arnoldrenderer.com/display/A5AFMUG/Round+Corners Hope this helps.
I sometimes use remesh modifier in Blender with small voxel size. It works pretty slow although. But you could then project UV from low poly on hi poly that impossible to do in Zbrush. It's not perfect on curved things although. And it's much easier to just bake Bevel shader node into low poly normal map as pior suggested…