1 year in on our Milestone, same story. Last camper we had was a 2012 Sunset Trail, it still did that after a decade.
That doesn't mean you can't do anything about it, it just may not be worth the work. As an experiment in the last camper I removed everything mounted to the ceiling in the back bunk room (lights, vent, and a cover plate for an unused electrical box) and put a thin bead of RTV on the back side of each item, making a sort of gasket. I let it completely cure (common trick with sealant if you want a gasket, but not a permanent one) then reinstalled the components.
It helped a lot but not completely. After three hauls there was no dust on any of the upper bunks/cabinet surfaces, but there was still some on the lower bunks. I traced this to rough cuts on the edges of the bunk supports themselves - the underlay under each bunk was OSB and dust from this would shake loose from the top bunks and drift down to the bottoms. So I took those out and coated the edges with epoxy to seal them.
After another haul I checked the back bunk room again and the dust was ALMOST gone except in one corner area. I later realized it was coming from the gap between the wall and ceiling where some thin molding strips had a gap. I sealed that with some caulk and after a few more hauls there was no more dust back there.
All told I figure I spent 10-12 hours sorting that out. I was able to do it. Was it worth it? Would it be worth it for a whole camper? Only you can decide that.
Lately we've been throwing thin plastic drop-cloths over the beds when we travel or store the camper. The thing is, even if you solve the sawdust issue, there's dust in the air itself. In a house, surfaces get used and cleaned regularly so it doesn't build up. But in a camper in storage for a few months over winter you'll come back to a thin layer of dust on literally everything. (We live in Colorado which is more dusty than other states, making it worse.) This is easily wiped off a counter but not as easily off a mattress. So since we wanted to cover the mattresses anyway for storage, we just do the same thing while driving. Each bedroom/bunk area has a plastic sheet that gets thrown over the bed when we're packing up, and we stopped worrying about it after that.