I think I’m looking at original floorboards, rotting underlayment on top of those, a delightful assortment of other boards on top of that, then Pergo flooring.
I’m unsure of the best way to proceed. My gut says to pull up the top layer of boards to remove that underlayment, but then I worry that that turns into ripping up the whole floor.
(Left Side cabinet)
(Right side wall)
The photo does not show any signs of obvious rot. Maybe add a moisture barrier underlayment before completing the floating flooring, the install your new cabinets.
If there is moisture, identifying it’s source is critical prior to applying a moisture barrier!
But yes, a barrier may be appropriate here.