Well unless there‘s a closed loop co2 - soy - animal - co2/methane - co2. Meat production will involve fossil fuels tho.

Not if the methane is produced through carbon from plants, in which case methane will stay constant but CO2 being sucked from the atmosphere would occur at the same rate as methane emission.

It's sourcing food from petroleum that causes the problem.

As the sibling already said: We're in a closed loop. Methane decomposes into CO2, so if you want to maintain a constant level of methane in the atmosphere, energy/mass conservation dictates that this carbon needs to come from somewhere else. Solution: It actually comes from the CO2, via grass growth & the cattle's digestive system. The amount of CO2, averaged over time, therefore cannot increase.

Cows don't eat coal or oil.