That article describes me exactly. I'm extroverted in terms of my cognitive functions, but as a 4w3 my Fi is almost the exact same score as my Fe according to two different tests (literally shy by 1/2 a point or 1 point), which makes sense since Enneagram 4s have such a high sense of valuing personal identity, individuality, personal expression, etc. That's probably why my Fi is so high, and I'd venture to say that enneagram 4 ENFJs probably also have high Fi compared to other ENFJs.
This is probably why we relate a lot to introverts' characteristics though we're technically extroverts. I always thought of myself as an ambivert, for I legitimately can get both energized and drained by social interactions. In the moment of the social interaction, I'm all fired up and can go on until I'm one of the last people at a party/social outing; but once I get home and have a break from social interactions, I spiral down into antisocial feelings and don't want to be around human beings for a long while, lol. So yeah, I definitely need my alone time. In fact, I'm usually in my own little world throughout the day, and I enjoy being alone in my little world. As a kid, I could easily play with other kids and make lots of friends (and was usually the leader in my group), but then I'd want to play by myself, and it left many of my friends feeling bewildered as to why i didn't want to play with them. It wasn't necessarily that, I just wanted to spend time in my own imagination. ENFJs already have vivid imaginations, so coupled with being a 4, I often find myself lost in my own head and enjoying the time there; that means wanting alone time.
I enjoy socializing and encouraging/inspiring people, but I'll admit I'm not as...determined about it as the stereotypical ENFJ. I want to be the life-changer in multiple people's lives (Fe), but I also have this strong need to be my own person and fulfill my own sense of purpose and destiny (Fi), and sometimes that sense of individuality wins out over the sense of being socially accepted—and sometimes, vice versa. It really is a struggle, trying to balance out being Fe-dom with an almost equally strong sense of Fi.
I've read that ENFJs already are "introverted extroverts", and that article definitely sheds light on that. I relate to a lot of the typical descriptions of ENFJs, but there are many nuances that don't line up with those descriptions. I'm sure there are other "introverted" ENFJs who feel the same.