That's temporary. It goes away during long term ketosis. I've been in ketosis for over a year and have found my endurance to be fine but my top end power to be decreased (cycling). I'm still competitive but I think if I was eating carbs I could add ~20% to my max power based on historical numbers.

Any tips on how to try keto as a mostly vegetarian individual? I am willing to eat eggs.

I use soy protein isolate, virgin coconut oil and virgin olive as my staples. I also eat 3 eggs a day. I'm around 10% calories from fruit but zero starch. You can play around with what works best for you but the first question I wild ask is why do you want to do keto? I do it due to an idiosyncrasy between my diet and my genetics which causes unbearable inflammation if I eat lots of carbs and sugar like a normal western diet. If I didn't have ankylosing spondylitis there is no way I would be doing this.

Since Keto is mostly fat that is pretty easy for vegetarians to source, no added sugar X nut butter and avocados sort out your fats.

For protein which in proper Keto should be kept at very moderate levels you can use any source of vegetarian protein you like, if you are willing to eat eggs it’s even better since you have a carb free source of protein.