Do you have carpeting or wood flooring? Decades ago, we replaced the wall-to-wall carpet in our bedrooms with hardwood, and there was an immediate marked decrease in the amount of dust.

There's deep pile carpeting in the living room area and low pile in 3 bedrooms, but they've been vacuumed numerous times.

I can't answer about the ducts. I've only been in this house 11 months.

Has this happened consistently during the 11 months or more so in some weather than others? Do you keep your windows open? Have you always had HVAC running or do you keep it off at times?

Same amount in different parts of the house? Is your HVAC constantly running or do you have times of the year when it is totally off and does that make a difference? Is there a crawl space or attic, and what is up there?

How often do you dust and what do you dry dust with? I use dry swiffer pads for all of my dusting - the rectangular pads meant to be placed on a floor swiffer. I fold them in quarters and use and throw at 5 of them away each time I dust our house.

What do you vacuum with? Does your vac have a good HEPA filter?

Same amount in different parts of the house? No, it's really bad in the bedrooms.

Is your HVAC constantly running or do you have times of the year when it is totally off and does that make a difference? I don't have central air, but it seems less in the summer.

Is there a crawl space or attic, and what is up there? Yes, I've never been up there but the home inspector was and took photos. it looked like fiberglass insulation on the floor of the attic (see photo).

How often do you dust and what do you dry dust with? I dust when I notice the buildup, about every 10 days.

What do you vacuum with? Does your vac have a good HEPA filter? I have a Panasonic canister vacuum with a HEPA filter.

Interesting mystery. I'll be curious when you share your solution. It's a very fine dust… like ash. So I have to ask what sources of ash you might have in your home (fireplace?) or outside. We lived near a city once that caused fine particulates in the air. I suppose volcanic ash or living near burning forests on the west coast. That ash can carry for miles. In fact I remember one time it reached the east coast here.  What circulates air in your home, or is it constantly still? Without ductwork there may be no filters to clean the air. This must be very frustrating, since baseboard heating is supposed to be so clean. There are air filters you can buy for your bedroom until you figure it out. If it's outside ash, planting conifers around your home can help. That is unless you are in the fire zone and that could be a fuel source. Although it doesn't look like carpet dust you may want to remove carpeting so you don't have to vacuum and end up just stirring it around. Tacky cloths are going to help get rid of it as you figure out the source. I'm just spit-balling here. Feedback on the part of the country you live in and any ash sources could help.

https://homeairguides.com/hepa-air-purifier-vs-ionizer-or-ionic-air-purifier/

I live in upstate NY in a fairly rural outskirts of a small town. No factories or industry and it's in a neighborhood of tract housing built in the mid-1990s. I don't have a fireplace or an air circulator and I live alone and don't smoke or have pets. Seems the heat is just ambient radiating from the baseboards. It would be difficult to inspect all of the baseboards since a lot of heavy furniture is in front of them now. Here are a few photos of the living areas:

This is the front exterior:

The furnace boiler in the basement:

I've found that the first few times the heat is turned on in autumn there will be more dust than usual. It's due to dust settling in the baseboard radiators over the summer and then becoming airborne due to convection. After about 2 weeks, everything is back to normal. I supposed it could be prevented by opening all the baseboards in late summer and vacuuming the fin tubes but I'm way too lazy to do that.

Dust is essentially three things (with no pets, no smoking, etc.): skin cells, textile fibers and pollution. My guess, given the pictures you have provided, your problem is due to dirt caught in the carpet and perhaps carpet fibers or residue. Wall-to-wall carpeting is notoriously filthy. Vacuums vary in their efficacy. You might try a pro carpet cleaning company.

Since you are in a rural area, it would seem to rule out pollution. However, even there, external causes are possible. My cousin lives in a very rural area with farm fields all around. On very dry days, as long as the ground isn't frozen and doesn't have crops growing, a strong wind picks up the dirt causing her house to get more dusty. It isn't even obvious that dirt is blowing around (nothing like a dust bowl), but the house is dustier.

You are only one person, but there is another possibility. If your previous abode had forced air heat along with a built in furnace humidifier, the air might have been moister compared to your current hot water heat with no humidifier. Do you notice that your skin is drier than before? You could be shedding more skin cells. One or two of the cheap vaporizers available at the drug store would help.

I have a mist vaporizer that I use in the living room in coldest months when the indoor humidity is the lowest (see photo), but that doesn't seem to make much difference. BTW - the previous owner had 2 Basset-mix dogs. I think she had the carpets shampooed before the sale - the carpets feel rough and stiff when I walk over them.

My last house I had to dust frequently. My present house doesn't need dusted often. Both carpeting except for the baths and bedrooms. The only difference is the last house had forced air gas heat and 2 1/2 miles from the city. This house is electric forced air and 12 miles from the city. So who knows? Since my present house is rural, has more vegetation than homes and less roads/traffic that is what I'm thinking is the reason for the reduction of dust.

I find dust is worse when the humidity is low. Try using swiffer dusters sprayed with end dust. It works for me.

The plot! She thickens! I love mysteries but only when they are sol-ved. 

A volcano in upstate New York...how you must have guffawed.

I assume you also cleaned the fins too...

With all those delightful figurines, the dusti is a serious issue.

I'm so sorry this mystery is so difficult.

https://www.thespruce.com/electric-baseboard-heaters-overview-1821912#:~:text=How far should furniture be,the farther away, the better.

I wondered if it might be a good idea to move furniture so the fins could be more easily cleaned and found the article from The Spruce that said placing furniture too close can be a fire hazzard.  I wonder if you would even be able to. You have a lot of furniture.

The safety thing relates to electric baseboard heat. Hot water baseboard heat has no such concern since the temps are way lower, although blocking too much baseboard will impact how well air can move over the fins to get heated.

Thank you so much for correcting me. So sorry.

I’m not knowledgeable about HVAC or baseboard systems,but perhaps there are filters that need cleaning. Since you have carpeting, I think I’d pay for a professional cleaning if you intend to keep it. When dusting, using swiffers or something that causes dust to cling should help. Perhaps another more powerful vacuum cleaner ( or having yours refurbished) will be helpful. I love my Miele canister, it’s going strong after 20+ years.
You say you haven’t been in your home long- if the carpet was there when you moved in, that might be the culprit. Wall-to-wall is notoriously filthy.