I mean it’s basically anything that massively affects your living situation or how you outwardly present / function as a person.

Want to live in a hole in the desert, or a cabin in the woods, or in a semi-legal squat? It would be pretty hard to maintain a relationship with a partner whose not also into living that way.

Want to convert the interior of your house to look like a Star Trek set? Better find someone that wants to live on the USS Enterprise.

Are you into extreme body modification? Better find someone whose alright with their partner surgically altering themselves to look like a Klingon.

There are also plenty of interests that are just risky or disruptive, like doing urban exploration, running a home chemistry lab, building tesla coils, etc. Tesla coils are just loud, urban exploration can get you arrested (though it’s unlikely anything of consequence will actually happen to you), and two of the amateur chemistry YouTube channels I watch have been raised by the police because the amount of glassware they bought set off an alarm (neither of them were charged with anything though). If you do any of those and your partner isn’t interested in them at all I can’t imagine that not being a pain point, considering that risk/disruption is also on top of you spending significant time / energy / cash on a hobby they have nothing to do with.

Finally, there are more benign hobbies like through hiking or immersive historical reenactment where, if your partner’s not coming with you, they’d have to be okay with you disappearing for weeks at a time and not being able to talk to them.