I have no idea whether this will work, but I think I've had two ads ever since I started using Windows 10 in 2015. The very first thing I did was to go through the Privacy Settings, pane by pane, to lock things down as much as one could then. I don't use the personal digital assistant feature of Cortana, and that might have an effect, and I do not return web search results in Windows searches.
But the thing I'd try is in the General pane of Privacy settings, and it's the first toggle: Let apps use advertising ID to make ads more interesting to you based on your app usage (turning this off will reset your ID).
Mine has been OFF since somewhere in the first week of the debut of Windows 10.
Brian - Windows 10 Home, 64-Bit, Version 1803, Build 17134
A little kindness from person to person is better than a vast love for all humankind.
~ Richard Dehmel