Methane tax IMO
The 'cows farting' story is not a major methane source.
https://www.nasa.gov/feature/jpl/nasa-led-study-solves-a-met...
I.e. there was major uncertainty that scientists were measuring more methane than they expected, and these scientists tried to figure out where it comes from.
The only thing your argument says is that for methane emissions from meat production apparently scientists had a pretty good idea about the numbers.