While I understand that there are many people whose idea of a conversation seems to be: "I say mine, you say yours". With that idea every interruption is a problem. However conversations are more than that and in my experience there are multiple legitimate reasons for interruptions.
E.g. if I am explaining a point that the other side already knows, it would be good that I read their nonverbal hints and realize they already know before insisting on rambling on for 15 minutes of monologue about a thing they already know. Heck, in that case it would be in my interest for them to interrupt me. And even if they don't know, they might like to say a thing as well, which is kinda a thing in conversions.
Or I am missing a foundational idea or a context clue that helps the other person follow, and you find out after you went into the explaination way to deep. In that case the interruption would help me catch that early on and I could adjust accordingly.
Now I am good at reading cues and knowing when it is time to give other people room to chime in. But I know many people who in a 20 minute conversation will have talked 95% of the duration and insist you keep interrupting, despite you having said 4 full sentences at max.
The point I wanted to make is that with such people, the only way not to interrupt them is by accepting they are holding a monologue and you are meant to be the audience, even if you already know the thing they are telling you. In some situations this can be okay, e.g. a friend who is pouring their heart out — they might need someone to listen. But in many situations this is just aomeone talking to bolster their own ego and convincing themselves of their own importance.
This borders on abusive behavior. If someone insists that in a conversation between equals their ideas are so important that the reaction of the other side doesn't matter and only one side is allowed to steer the conversation, they are forcing that on you.
Not to say there aren't negative interruptions as well. E.g. someone who rarely speaks outlines their perspective and the guy who has to monologue all the time keeps interrupting, because he can't stand to listen etc. Totally hate that.
But in my experience most people who complain about interruption are people who dominate conversations in terms of talking time. Our goal should be to defend those who don't complain and see the nuances of the whole thing.