Beans and rice are going to put you into malnutrition sooner or later, lack of micronutrients. The nice thing about meat is that you really won’t have to care about that one.

If you never switch that up, yes. But fortunately there's a lot of other cheap plants you can use. So you can avoid most issues by simply switching it up once in a while. And thanks to a long history of improving the seeds soy now has a comparable biological value to eggs (and beasts most meats). Hence those will work well as a start.

If you're a woman or lose blood for other reasons, you'll likely want some iron supplements, but those can be avoided if you really want to.

B12 however is the one thing you need to take as a supplement if you try to live of plants. So I don't get why you use mention that. It's in any vegan-diet starter post and while it's theoretically possible to obtain enough on a vegetarian diet via milk, consuming that much dairy defeats the purpose of vegetarianism hence most take those pills as well.

True. But continuing to subsidizing meat (without those it would never have been affordable) is the least efficient way to go about it. Saving the money (if we include the environmental costs we're easily in the hundreds of billions per year for Europe alone) that goes into subsidies for livestock, could pay for a lot of programs that make plant-based healthy eating more widespread. By education, but also by targeted subsidizing of healthy foods.

Edit: Also: Meat being take off the menu by prices makes it more complicated to obtain amino acids, but it also has a lot of positive side effects. Red meat and especially processed products cause quite a bit of problems. Heck, maybe we should bring back rationing.

Have a look at e.g. https://www.bbc.com/news/magazine-11864290. That was only a fun self-experiment, and not a scientific study at all, of course.

But who was mentioning the population of the whole world? This is a channel about Europe, linking an article about Europe.