I wish people would stop saying attics or buildings need to breathe - it’s just not true. People need to breathe; building assemblies made of materials that can rot need to stay dry. One way to keep them dry is to give them space to dry into, and that is often achieved by venting. However, all vents need to be outboard of insulation (on the side that’s cold in winter). Any insulation on the outside of a vent is doing as much good for a house as it would do sitting on a rack at the lumber yard.

Attic vents are not for cooling; they are for venting moisture out of an attic space. Venting has roughly zero effect on the temperature inside an attic or on the temperature of a roof deck.

Old-timers (people who were around when insulation started to become common in the 1900s) came up with the notion that houses needed to breathe when paint started to fall off of the siding on walls that had recently been insulated. The issue was vapor pressure, not inability to breathe, but folks back then didn’t know any better. There’s been about a century of research on building science since then. Anyone interested in the topic can look at the decades of research done by Building Science Corp., or for a crash course, check out the recently published book, “Houses need to breathe - or do they?” Spoiler alert: I gave it away up top. (Edited to consolidate two comments in one for clarity)