We have know that Vole has been testing such ads and promos in File Explorer and Microsoft Store on Windows 11 and these have gone down as well as custard flavoured with live parana.
Microsoft, however, does not appear to have got the message and is trying to put ads into the Windows 11 Start menu.
Twitter user Albacore noticed promos for OneDrive on the user session flyout in Start menu recently on the newer Windows 11 Dev Channel builds. The promo says "Back up your files" with a OneDrive logo.
More such promos have also been noticed, with another one suggesting signing up for a Microsoft Account (MSA). It is possible to disable the adverts, and if Microsoft does make this an established feature, then the only people seeing the adverts are those who cannot do a search to find out how to disable them.