For me there’s two separate participants, a ‘talker’ and a ‘listener’. My mind identifies more with the talker, because that’s the one that has agency. Since there are two participants, both of which are me, I talk in 1st person plural (‘we’ve got to do …’, 'we thought about this earlier’). I stopped being afraid of being alone after I started having an internal dialogue around the age of 11, since having a second participant in the conversation meant I was always in company.
Edit: Wow, looks like there’s a lot more diversity in this than I was expecting
When I’m not thinking about anything, it just plays music, all the time.
When I’m thinking, it’s kinda like the reasoning of an LLM, it talks about possible ways to solve something, how things could end, and says things like “oh right, if I do X, I need to do Y”.
The strangest thing is that despite me being italian, most of my inner monologue is in english, especially when I’m playing games or programming; and it’s not in my voice, it’s a generic male voice that kinda sounds like Morgan Freeman.