I don't remember doing anything to any settings regarding ads. I clean installed Windows 10, 1903 on August 31, 2019. The only ads were the ones on the Start Menu that come bundled with the OS. Other than that, I haven't seen any ads in File Explorer, Notifications, Start Menu, etc. Googling ads leads to sites suggesting how to turn them off. When I go to those settings, I have them enabled by default. Is it because Ads aren't supplied by Windows 10 in my country (don't know for sure)?