I do see Grammarly ads if I search things like "practice or practise" because I write English every work day.

Well, I use Firefox account containers and auto cookie delete everywhere. So Youtube knows little about me writing English.

Many people outside the English-speaking world will never see those adds. Your search bubble is not others.

Despite that, even in the search bubbles containing Grammarly I doubt closing an account with 3 videos will do any significant PR damage to anyone.

So what where the videos about? Grammarly storing everything the user writes??? Selling it to others???