Prompts to buy additional products do not make a company an advertising company. If it did, every restaurant in the world would be an “advertising company” because wait staff, cashiers, and menus encourage customers to order additional food.
1. Apple Displays ads (Sales content for products.)
2. Apple gets paid when those ads convert into sales.
If Apple didn't get paid when Apps were sold through the app store, then I could see how it isn't an ad platform for them. Yet, the only option, if you want to sell a product listed on the app store is to pay Apple their cut, which fundamentally turns it into a paid advertising platform controlled by Apple.
But it's a channel cost not an advertising one.
Apple still gets their cut when an in-app purchase is made hence it's not tied to the App Store list.
Even if rank and file Apple employees do not want to grow ads in iOS/App Store, clearly Apple leadership wants to sell more ads (and increase their services revenue). At App Store scale, their volume of ads is not trivial.
IMO, both Microsoft and Apple are showing me ads I don't want to be shown.