“In March, with the KB5023778 preview build, Microsoft began sending them out to a few users, with the promise the practice would be more widely deployed in the following months.”
Insider build 23435 adds Start menu “badging” for anyone on a local account, pitching a Microsoft account with backups, settings sync and free Microsoft 365. Microsoft calls these notifications, not ads. The target is the user who chose not to sign in. An operating system you paid for now nags you to hand over an identity so it can sell you cloud storage.