For me, my mental energy and alertness levels are more stable, because I'm avoiding the blood sugar roller coaster that I get from eating sugar/carbs.

When I eat carbs, most of my day is either "I'm so hungry I can't think", or "I just ate, food coma", and I'm only alert and maximally productive for the brief time after the food coma wears off and before I get hungry again. With keto, hunger and fullness are less distracting feelings that don't impact my attention as much.

People often say this, but I'm not yet convinced it has a fully or even partially physiologic basis.

One way to do an experiment would be to fast someone for 48h (about when you completely run out of glycogen, and ketones start to ramp up from fat catabolism), and while fasting, infuse glucose, blinded, into them. I wonder whether people could tell whether they are getting IV glucose or IV saline, just by how they feel. Maybe someone already did this experiment.

Where can I read more about that type of diet ?

Dunno if it helps, there's a lot of discussion over at https://www.reddit.com/r/keto/

Generally, a big improvement in ability to focus, and a sustained mental clarity throughout the day.

Entering in ketosis was also an watershed moment, like an epiphany, with a sudden feeling of increased awareness. But it's hard to describe precisely, and I guess YMMV.