Full disclosure, I work for Google opinions are my own etc etc
The LLM built into YouTube is one of the few LLM chatbots bolted onto existing apps that I actually find useful. Not just for summaries but questions like "what is the timestamp in this 2 hour video where they talk about _____".
I thought it was for everyone my bad. Turns out except for some educational videos it's just for premium subscribers with certain location/language combos (you can probably guess which...)