Any insulation you put on the floor is usually (and I'm no expert) rigid foam or a dricore like product that creates an air pocket through separation. Neither will really level a floor on its own and shimming dricore all over the place can be a real pain to work out the wobbles.
If money and ceiling height weren't an issue, I'd have spent the time installing framing sleepers to level things out, a new subfloor on top, then the new flooring...
Ref.
Framing Sleeper Floors - Preparing the Floor - Flooring Prep Installation. DIY Advice
But, for me, that was a hell of a lot of work for very little gain. I reasoned that as long as the floor was true -- that is, not level but with a consistent slope to work with -- then flooring material could still be applied. So my bathroom space has a slope, but I used dricore tiles and a few shims to get it true enough to lay lino on top...
While my wet bar is level atop the dri-core subfloor which is not...
Carpet covers the majority of the open space, unlevel as it is, and I'm willing to live with it that way.
But if you want that vinyl plank across a whole floor, you'll definitely have to do something to reduce the floor's imperfections.
I've probably made things worse now... 8)