That is completely misunderstanding the study. The study still finds that food emissions alone - with zero emissions from non-food sources after 2020 - would make us miss climate targets.. They do other analysis later than only makes the picture worse if other emissions aren't immediately stopped

As such, even if all non–food system GHG emissions were immediately stopped and were net zero from 2020 to 2100, emissions from the food system alone would likely exceed the 1.5°C emissions limit between 2051 and 2063

For biogas, it still has plenty of methane emissions and doesn't solve a number of other environmental issues like waterway pollution

What "medication" are you referring to with cattle? That's pretty vague but most likely you are referring to some kind of feed addatives which have the problems I mentioned earlier