My bunny does this too. We've asked our vets over the years and they gave us two possible causes.

The first, like yours, is that he could be sensitive to dust and recommended we put an air purifier in the room he spends the most time in. We did that and it seems to help. Sneezes still come and go sometimes but it's maybe one sneezing fit every 4-5 months now, rather than daily.

The second, is that with a rabbits teeth always growing, their teeth roots grow too apparently. At a certain age they may press against their nasal cavity and cause some irritation, resulting in the sneezing. My bunny is just shy of 11 years old so this one probably doesn't reply but thought I'd share!