They're not typical in the United States; one-piece comforters are more typical.

I'm from Québec and we/some put thick bed covers like comforters on top of another set of thin sheets. I grew up with the principle of just removing a layer if it was hot in summer, sometimes removing the comforter entirely, and putting it back in winter. I have never used a duvet before visiting Europe. It's only when I slept in hotels in Germany that I met a duvet for the first time of my life. Most of them only have a single sheet, a duvet and a giant deflated pillow. And I must admit that I hated it. So much so that I went to Decathlon to buy a liner and an inflatable pillow because I couldn't sleep with the duvet nor the folded pillow.