Proteins are just amino acids. You can find the same proteins in plant foods as meat. There are other details about what different types of basic foods contain, of course, but it’s theoretically possible to create something that contains all the same nutrients as meat out of plants.
Well, check it out: https://vcahospitals.com/know-your-pet/taurine-in-cats
Taurine is an amino acid that’s an esssential nutrient for cats.