If CO2 attracts the creatures, couldn't they wear masks?

For some reason the movie acts like they know nothing about the creatures sometimes, and other times they know what attracts them. I mean, they kept running around with guns and shooting at them, then act surprised when the bullet just bounces off. Pretty dumb.

A mask is no filter for what you exhale, unless it's a fully autonomous suit with an oxygene tank on your back.
A mask will shorten the range of how far your breath will reach, something like shorten 8 meters without mask to 2 meters or so with mask, but it will not mask your presence.

That's why masks work against air born viruses like the flu or Covid in areas where you get closer than 8 meters to infected people, but they do not work anymore if you get closer than 2 meters.
But keep in mind, non infected people wearing a mask doesn't protect anyone, infected people have to wear masks to limit the range of the viruses they spread.