(Photos above aren't mine just examples)

Hello, recently my tabletop desk was damaged in a move and I would like to finally do the IKEA hack with Alex Drawers with risers and a white Saljan countertop specifically the 74inch version. I have seen some people put a leg in the back middle but I am unsure if that truly would prevent sagging in the middle and I do want to put my tabletop on risers specifically the black ones on the second image. So what I am looking for advice, opinions, instructions etc. to prevent sag with the risers. I have seen some post where people install some sort of metal beam or scaffolding but I'm unsure if something like that would work with the furniture risers. I would also like to leave the underside of my desk open to installing cable raceways and places for surge protector if possible. And have it be something I can disassemble and reassemble if I ever have to move.