This quickly becomes a definition problem (asymptomatic, presymptomatic, maybe even "sub-symptomatic").
At the very least, spread by people who either don't know they are sick, or don't think that their symptoms are Covid is a significant problem. It probably is our most significant problem in terms of spread.
This is why the single biggest policy thing we could do is have antigen based testing approved and implemented immediately. But we don't have that, because gov'ts are bad at things.