Ikea Kallax - maximum load capacity

If the thing stands on the floor, then put a board on it so the feet can't press through the surface and that's it.

But Kallax can only hold 20 kg, the microwave weighs 21 kg empty. Or does the weight distribute better with an additional board? Although the Metod you mentioned is of course cheaper than a KALLAX. I hadn't considered it before.

I think the load can be significantly higher if the item is standing on the floor and something is on top of it. The microwave definitely has 4 small feet with an estimated area of 4 cm². Since pressure is known to be p = F/A, this will be quite high. Whether a thin hardboard would withstand this, I would not want to try. You can also calculate it and research with manufacturers.