Does anyone else not really like talking about their special interests?

I can see how bored people are the second I start, like their eye contact suddenly breaks and they look around the room, and only say “mmhmm” instead of replying. So I shut up after one sentence.

But if the other person also likes the subject, I don’t like talking to them either, because there’s nothing to say. If we disagree I don’t want to be rude and argue so I awkwardly pretend to agree. If we agree then all you can do is tell each other things you both already know and agree that they’re good.