In the past year I had interviews with a couple of US-based IT companies for a technical role at their European offices. The interviews were eerily similar: phone from HR, coding interviews over video call, then on site interviews: coding, architecture design and "behavioral" interviews. In each behavioral interview I received a question:

Tell me about a time you had a conflict at work

The thing is, in my 20 years of work I don't remember ever having had a conflict with anyone. This is what I told the interviewers and they didn't seem to be satisfied with this answer. I've been married for 10 years, never had a row with my wife (I also told this to one interviewer). I don't know what to make from this question - I understand they want to know my conflict resolution skills, but I honestly don't remember I needed these.

Maybe it's a cultural thing, in US-based companies conflicts are more common than in the European companies I worked so far? Also, I'm fairly introvert, maybe that's why conflicts and me are avoiding each other. Anyway, I looked up some examples on Google for this question, but they don't seem to apply to me (for example I never had people reporting to me; no manager ever "blew up" on me).

Even if I'd face a conflict, I can't imagine any other solution that to "talk with the other person and if we still disagree, go to our manager". How should I answer a question like this?