I have Windows 11 Pro and I've never seen an ad. I don't remember turning anything off but I did upgrade from Windows 10, so maybe that had something to do with it, unless it's just that Pro doesn't contain ads. I also don't use it with a microsoft account and don't have any "services" from them, so maybe that helps.
I'm curious about this, as a Windows 11 pro user, myself. Do you already have a Microsoft account, use OneDrive, and pay for Office 365?