My wife loves genealogy and like to tell me about interesting discoveries and how she sleuthed them out. I don't care, but I love hearing her talk about it.
She also has a couple thousand romance novels which she like to tell me about. I do not read romance novels, but I enjoy our conversations about the stories, especially the historical ones, because she's so enthralled.
Being swept up into someone else's hyperfocus is refreshing. It builds the bonds of friendship. It shows a great deal of trust.
It's like reading stream of consciousness literature: you feel like you are part of something happening in real time.
Edit: I said "I don't care" about genealogy which is kind of dismissive. I am not super excited about where I came from or from whom I am descended. It's interesting, but not something I would spend any amount of time figuring out. She can spend hours scouring through old newspapers and cemetery records online. She loves it. That's what I mean. I don't care to do all that. I do actually care that my wife really enjoys it. I love that she enjoys it and is able to do it. She had to stop for a couple of years due her chronic migraine and is only slowly getting back into it.