I can ride all day, day after day, fasted. In fact I'm planning a cross-Canada ride (hopefully 2023) where I expect to ride fasted every day. The challenge will be to able to consume the calories I burn off daily in just one meal. lol
I haven't bonked once since all but completely eliminating carbs. Used to bonk - a thing of the past now. Gladly.
If your liver (and possibly kidneys) works properly it will produce all the glycogen you need as long as there isn't an external source to interfere with the production.
Keto is as much a "fad diet" as cycling is a "fad activity"