Stroller Blanket I See Parents Place Blankets/comforters On Top Of Baby Carrier Or Stroller - Is Baby Getting Enough Oxygen?

I see parents place blankets/comforters on top of baby carrier or stroller - is baby getting enough oxygen? - stroller blanket

Sorry if this is a silly question, but I was always worried about her. Are there any risks associated with this common behavior? And if he is drowning under the cover and not heard?