Humans evolved to depend on the amount of protein and calcium naturally found in a WFPB diet.

https://www.jeffnovick.com/blog/the-perception-problem-with-protein
It is very easy to get enough protein, and impossible not to, if you follow these three simple guidelines:

1. Consume enough calories to maintain a healthy weight.
2. Eat a variety of whole natural foods including plenty of vegetables, starchy vegetables, whole grains, beans, peas, and lentils.
3. Greatly limit or eliminate empty calories.

Eating added sugar and added oil (empty calories) displaces nutritious whole food. If 40% of a vegan's diet is empty calories, then they are eating 40% less protein, calcium and other nutrients (40% of the Standard American diet is empty calories).

Protein and calcium myths:

• https://nutritionfacts.org/video/the-great-protein-fiasco/
• https://www.forksoverknives.com/the-myth-of-complementary-protein/
• https://nutritionfacts.org/video/is-milk-good-for-our-bones/