Creating a gameplay system which mixes Xcom combat with open world gameplay (Like Mutant Year Zero)

Hi all!

How would one go about making a gameplay system like Mutant Year Zero which mixes open world gameplay with Xcom styled combat (Turn based + tiled system)? A couple of us were thinking of making a demo with this same style but are just trying to figure out how we could get it to work. One idea was to make an invisible tiled grid in the world which characters can snap to as soon as they begin combat. And whilst in open world mode, they could just freely walk everywhere. Does anyone have any ideas on how we could technically get this to work? Any things we should be aware of with a gameplay system like this?

I have posted some links below of Mutant Year Zero for reference of what we are trying to achieve:Mutant Year Zero: Road to Eden | Project Spotlight | Unreal Engine - YouTube