Reply by Ben

Kind of like this?

or like this?

if you’re trying to add character, 2×4s and sheetrock isn’t going to do it.
I would essentially build a small cabinet either side, and put a short column on top.
Or, build the cabinets and make a post out of trim boards that runs floor to header (as in the second picture). Then just trim it all out nice.

Another option would be double french doors.

If you just want a cheap separation, then yea, slap up the 2X4s right on top of the existing sheetrock, use 3” deck screws like A1 says, and sheetrock over it all.