As long as he isn't making your repeat it back or testing you on it you can nod and tune it out. My son knows I do this but he has accepted that his need to talk is stronger than his need to be heard and so it's the compromise. When it's really important to him that I listen he will tell me that he is going to quiz me on it later. And he usually does
And, yes, he is also discovering that his memory of the facts isn't always as accurate as he thought.
We've had a lot of talks over the years along the lines of "I know you find all that interesting but it just isn't my priority right now" or "I can't keep these types of details in my head and with the internet there really isn't any good reason I need to" or "its great that you like to think about these things but the truth is I'm just not interested in them the same way you are."
We also used a hand signal for a while when he was first practicing pragmatic speech with his therapist. To let him know when he was talking on past the interest of his listener and/or starting to repeat.
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Mom to an amazing young adult AS son, plus an also amazing non-AS daughter. Most likely part of the "Broader Autism Phenotype" (some traits).