I really wanted to be vegan for personal reasons, but looking at the evidence makes it hard to argue that humans evolved to be based purely on vegetables. There are a whole lot of factors to take into consideration regarding nutrition, the main one being how it affects your microbiome.
wrt testosterone, eating fats is a huge part there, but you could probably get great ratios eating flax seed, avocado, coconut oil, olive oil, and a variety of nuts. Sourcing matters-extra virgin cold pressed is better, and the less processed the better. However that comes with a cost of your body not digesting the nutrients as easily, as there are more antinutrients in the food.
Meat is much more easily digestible, and apparently has better protein ratios than plan protein. I also find some evidence pretty persuasive that humans are built to be preferential to meat (shorter long intestine, higher stomach acid ph). But we're omnivores. Unless you have a specific autoimmune disorder, full carnivore is probably unnecessary.
One nice thing I recently found out is that you can test Testosterone pretty cheaply for like $50, so if it's something you want to experiment with, you can take a baseline T reading, then try adding meat, and take another reading in a month, and then again in two and three months. If you see a significant change, you'll have your answer for you. Nutrition is highly individual due to the gut microbiome being extremely unique to each person based on a lifetime of eating habits as well as initial seeding from when they were a child.
Regarding meats, make sure they're antibiotic free, pasture raised, and if they're ruminants (grass-eating), that they are grass fed and grass finished. This nearly guarantees optimal omega 3:6 ratios.
All this is to say that it's complicated.
One last unrelated thing is the benefit of adding in fermented foods as well with live and active cultures, much more so than any probiotic pill. Kimchis, sauerkrauts, kefir, yogurt are all great. Great for your body all around.