Substantial how? Apple doesn’t sell ads and I’m pretty sure that antithetical to their business model, if they did their advantage in other ways (privacy which sucks anyways) would dry up.
Apple build advertisement profiles on iOS users, and allow App Store and Apple News ads to be targeted using said profiles. They are estimated to sell billions of dollars of ads per year. Their tracking is, as far as I can tell, not opt in. Instead it's an opt-out hidden in an obscure settings menu, with the sign "beware of the Leopard" on the door.
So it absolutely isn't antithetical to their business model. The opposite: Apple's business model is to lock users to their platform, and extract rent out of as much of their economic activity as possible. If anything, third party advertisers making money from iOS users directly without giving Apple a cut is what's antithetical to Apple's business model.
It seems basically guaranteed that within a couple of years Apple will be doing another attempt at launching an ad network for third party apps and/or web sites (Safari-only) using the same tracking data.
See https://support.apple.com/en-us/HT205223
So it absolutely isn't antithetical to their business model. The opposite: Apple's business model is to lock users to their platform, and extract rent out of as much of their economic activity as possible. If anything, third party advertisers making money from iOS users directly without giving Apple a cut is what's antithetical to Apple's business model.
It seems basically guaranteed that within a couple of years Apple will be doing another attempt at launching an ad network for third party apps and/or web sites (Safari-only) using the same tracking data.