I’m sure it depends on how you define intelligence.

I’m sure there are people without internal monologues who can solve any problem you put in front of them. But I do think there is a certain level of emotional intelligence that can’t exist without an internal monologue. I suppose one could externalize this process and just talk aloud to themselves in order to mull something over. But even then, you likely couldn’t do that all day every day. Those of us with internal monologues must glean some sort of benefit from essentially self-reflecting all day.

Granted, all of this hinges on my limited understanding of consciousness being somewhat accurate. It’s possible that everyone has an internal monologue and some people just lack a connection in their brain that brings it to the forefront of their consciousness. Maybe some people’s IMs are in their subconscious and inform their actions in ways they simply aren’t aware of.