Have a look on any of the big supermarkets' websites - search vegetarian or vegan - there are lots of vegan and vegetarian protein options. I'm relatively new to the vegetarian way of eating but I'm finding tofu, textured vegetable protein products, Quorn, seitan, tempeh, lentils and pulses - all in moderation keep me in the keto range, giving me plenty of protein with a level of carbs that I am currently producing keytones. Its just a question of wanting to eat this way enough (for whatever reason) and then searching for protein alternatives and being open to solutions.
There seems to be a detailed explanation of the Karbeto diet on the website at this link https://www.reversediabetes.com.au/the-karbeto-diet-way-to-reverse-diabetes.htm - it seems to be a short term diet used at the start of the program, so that blood glucose doesn't spike up when eating carbs but then when insulin sensitivity improves, normal complex carb foods are introduced. interesting !