Yes, following a keto diet can reduce exercise performance in events requiring maximum or near-maximum effort . However, the keto diet appears to be less detrimental for low and moderate-intensity exercise after the adaptation period.
The keto diet is a high fat, very low carb eating approach, where carbohydrate intake is restricted to less than 50g/day. Studies have found that those on a keto diet performed 4-15% lower than those eating a high carbohydrate diet . In addition, athletes on a keto diet experience early onset fatigue during short-duration activities .
While keto may be less detrimental for submaximal exercise, athletes may fall short on nutrients such as fiber, calcium, magnesium, selenium, vitamin C and B-vitamins which can potentially impact performance. For more information on the ketogenic diet for athletic performance check out this article.
 Wroble, K. A., Trott, M. N., Schweitzer, G. G., Rahman, R. S., Kelly, P. V., & Weiss, E. P. (2019). Low-carbohydrate, ketogenic diet impairs anaerobic exercise performance in exercise-trained women and men: a randomized-sequence crossover trial. The Journal of sports medicine and physical fitness, 59(4), 600–607. https://doi.org/10.23736/S0022-4707.18.08318-4
 Chang, C. K., Borer, K., & Lin, P. J. (2017). Low-Carbohydrate-High-Fat Diet: Can it Help Exercise Performance?. Journal of human kinetics, 56, 81–92. https://doi.org/10.1515/hukin-2017-0025