By the way, all plant foods have all amino acids. They just have them in proportions to one another that don't quite match the proportions that we need. But this is only relevant, if you eat the minimum amount of protein necessary to sustain your body tissues.
In a Western diet, we typically eat significantly more protein than that. As such, if e.g. black beans only provide 50% of an amino acid compared to the other amino acids and compared to what we need, you can totally eat 200% black beans to make up for it.
Or, what's more likely the case, you're not gonna eat just black beans, but rather mix and match them with lots of other protein sources, which will have different amino acid distributions. Even wheat and rice contain protein. Well, and then you're gonna eat significantly more of that mixture than you actually need, so you don't need be particularly cautious at mixing+matching either.

Not the most scientific source, but has some decent illustrations: https://vegfaqs.com/essential-amino-acid-profiles-beans/

Huh, isn't duckweed pretty easy to grow?

Over >50% of the space humans occupy is for agriculture

i think it's more like >90%.

i.e. of the area that is used (Agriculture, Urban and Built-up Land),

• urban and built-up land is 1m km²,
• agriculture is 48m km²,

so agriculture is 48 of 49 millions km² used, that's 98%. The remaining 2% are for streets and housing.

complete amino complexes and b12

Tis a question of "how much of it can be absorbed by humans".

For example absorption rate of vitamin A from animal sources is ~90%, but about 10% from veggies (if you use vegetable fat it's a bit higher, animal fat even more higher, cook it, juice it, the absorption rate plateaues at 30%; and technically it's not a vitamin A but something that will become a vitamin A when dissolved in fat) - and the amount of it in veggies is lower compared to animal byproducts.