How to fix a cupboard to 32mm thick plasterboard
It's probably double 5/8ths drywall, I'd use toggle bolts. And then washers and 3" deck screws to the stud for safety (not drywall screws), even if you're going to do all four corners with toggle bolts. There should be some one-by inside the cabinet at the top (and possibly the bottom) this is where you want your fasteners penetrating, not just through the flimsy back panel. Your local hardware store should have these:

1/4" x 4" Toggle Bolt:  (tannerbolt.com)



You can skimp on diameter if you want, but the shorter they are, the harder it's going to be to install all four at the same time. The size shown is my go-to.

Hand tighten only, or you risk stripping the tiny nut in the spreader or compromising the drywall integrity. You need to be able to feel what's going on in there; they should just be snug.  Be extra careful with smaller diameter toggles as they have even wimpier nuts.

Other types of drywall fasteners are discussed here: What benefit do plasterboard drywall screws have?