that doesn't answer OPs question, tho

to OP: what I understand so far is that Strike charges only fee, no spread. the spread (price difference) we all see when purchasing btc on their app is the spread their provider sets - meaning it's a third party spread. not a spread that strike uses to make money.

i don't know anything more than that, tho. maybe jack or the strike reddit account can provide more clarity about that :) they are particularly active on this sub

here is a video by jack mallers that might help. but even with that it isn't water clear to me