Cow methane is completely net zero already. Grass converts CO2 into cellulose. Cow eats grass. Carbon in cellulose metabolizes to methane by bacteria as part of healthy ruminant digestion. Methane is released into the air where over the course of maybe a decade it reacts with oxygen to produce CO2 and water. That CO2 is the EXACT same amount of CO2 as was converted into cellulose to begin with; we know this because conservation of mass is a thing.

While I'm not all fucking panicky about fossil fuels there is a huge difference between releasing sequestered carbon that (sort of) sticks around and the natural carbon cycle that we all learned about in elementary school.

The only reason it would ever be a concern is if the population of ruminants was growing rapidly (because that would mean a higher steady state for methane), but that's not the case. We're kind of at peak cow. The Americas is about full up with cows, and it barely replaces the natural ruminant population that's been greatly reduced. Africa is currently well below it's natural ruminant population because many natural ruminant populations have been greatly reduced without replacement with livestock.