It's a false equivalency to claim there's nothing we can do here. Emissions are significantly less large for eating plants directly compared to raising farm animals

Transitioning to plant-based diets (PBDs) has the potential to reduce diet-related land use by 76%, diet-related greenhouse gas emissions by 49%, eutrophication by 49%, and green and blue water use by 21% and 14%, respectively, whilst garnering substantial health co-benefits

[...]

Plant-based foods have a significantly smaller footprint on the environment than animal-based foods. Even the least sustainable vegetables and cereals cause less environmental harm than the lowest impact meat and dairy products [9].

https://www.mdpi.com/2072-6643/14/8/1614/html least

Decomposition gives off greenhouse gasses like methane, so even they aren't neutral.

Transportation is a tiny portion of any agricultural emissions, it's really producing it in the first place that matters. If global consumption levels don't reduce, then this is just an accounting shell game with emissions happening elsewhere

Transport is a small contributor to emissions. For most food products, it accounts for less than 10%, and it’s much smaller for the largest GHG emitters. In beef from beef herds, it’s 0.5%.

Not just transport, but all processes in the supply chain after the food left the farm – processing, transport, retail and packaging – mostly account for a small share of emissions.

This data shows that this is the case when we look at individual food products. But studies also shows that this holds true for actual diets; here we show the results of a study which looked at the footprint of diets across the EU. Food transport was responsible for only 6% of emissions, whilst dairy, meat and eggs accounted for 83%.

https://ourworldindata.org/food-choice-vs-eating-local

New Zealand needs larger reduction in cattle sizes than just a 10x in many areas for other environmental impacts. For instance, the dairy production in Canterbury is so high that there needs to be a 12x reduction in size to keep water at safe drinking levels because of its nitrate pollution

The large footprint for milk in Canterbury indicates just how far the capacity of the environment has been overshot. To maintain that level of production and have healthy water would require either 12 times more rainfall in the region or a 12-fold reduction in cows.

https://theconversation.com/11-000-litres-of-water-to-make-one-litre-of-milk-new-questions-about-the-freshwater-impact-of-nz-dairy-farming-183806