YouTube video from VirtaHealth.com about exogenous ketones in athletic performance. Among other things it shows that muscles adapt to using ketones. Interestingly, executive function definitely improves with ketones (around 19:00 minutes.) A lot of the benefit may come in recovery.
The talk is a little technical but not beyond comprehension and only fair in presentation quality.
This chart of energy sources is pretty well known, but nicely presented. The longer one exercises, the more one shifts to aerobic metabolism (burning fats).