Like everything else, it depends. In the extreme case, if you eat beef every day but use a bicycle for transportation, live in a mild climate with little need for heating and cooling, and rarely fly in an airplane, your diet could be a significant part of your carbon footprint in percentage terms.
Eh, it's just that the entire supply chain that keeps them alive means that their per-capita carbon footprint is almost certainly not dominated by their diet, let alone by beef alone (it's an outsized fraction, but it's just not that significant compared to other stuff). But yeah, hard to talk accurately in broad strokes about a very varied audience.
In this case, they said they live in Rome. Concrete, heavy machinery to make it livable, trash movement, maintaining their public transit, household goods, electricity via nat gas, etc. Sounds like they're making a good effort, though, and in terms of just the discretionary part, they might be right.
That says 14-18% of global GHG emissions is due to cattle, the person I was responding to said "the biggest impact you can have is by eating way less meat, cattle in particular". That doesn't seem like the biggest impact possible. For Americans, their entire diet is attributable to about "5.14 kg CO 2 eq. per person per day" https://habitsofwaste.org/wp-content/uploads/2020/11/2020-CS... (UMich Center for Sustainable Systems). For a family of 2.5, that equates to about 4.5 tons CO2e/year. The average American family footprint is about 48 tons CO2e/year. So slightly less than 10% for their entire diet. Of that, maybe a bit more than half is attributable to cattle, or 5% total.
By comparison, driving a pair of gasoline cars their average of 10k miles/yr is something like 16% of the average American family's yearly emissions, or 3x the beef.
Switching from heating with natural gas to a heat pump would also make a bigger dent for the average American family, let alone if they're living somewhere that gets properly cold, like New England. Or just spending $2,000 on air sealing and a layer of fiberglass, for those living in a leaky house - more impactful than not eating beef.
Looking into it a bit for Italian families, it looks like cattle might a larger proportion, partly because their overall carbon footprint is lower. But it's still a relatively small proportion (<15%).
Pretty sure if landowners weren't raising cattle, the alternative isn't going to be letting it return to nature and lowering the value of their land, without big government programs that essentially pay them to do that, so that whole thing seems kind of moot.