But dust falls vertically, so flat on your desk will be optimal position I would guess. A narrow space with enough room for good air flow. The previous version benefited from a vertical stand more because of it's footprint.Put your Mac Mini in a vertical position instead of horizontal. The air is sucked in from the bottom and expelled out the top. It's easy to clean where the air get taken in in this position, to keep the dust down. The metal sides of the mini also have more opportunity to dissipate heat in this position, so it runs cooler.
Sturdy heavy metal stand twenty bucks on Amazon. Or it was until the Trump tariffs...