Someone else linked these in the replies, but that's simply not true. Most land taken up to grow plants is used to inefficiently feed livestock. Feeding humans plants only would be much much more efficient in terms of land use.
Because it is just not suitable for growing crops that humans can realistically consume. If you can figure out a way to change this at scale, it'll be a discovery on par with Haber's process w.r.t. impact on human civilization.
I think we can eventually get there, as evidenced by billionaires and real estate companies buying up bad farmland over the last decade or so.
But in a way that may be different from what you'd expect. The same crop yields both soy milk/oil/tofu/sauce and then the end products after extracting all that goes into animal feed.
Without the need to feed animals maybe this can be repurposed for bio-diesel or ethanol similar to corn, I'm sure there's some way to make that economically viable with enough scale. But this doesn't really free up much land to produce human food with.
All land is not equal. And unless you subscribe to 'interesting' ideas like forcing the world to survive on insect paste, either animal farming is here to stay or we cut down a bunch more forests.
Feeding the world is technically easy, there is more than enough space for growing crops. The only reason that it's not done is the desire to eat meat and the lack of any real will to do it.