Listening to an episode of the Double Pivot Podcast (an analytics-focused football podcast) about Hojlund from a few months ago where they broke down his stats profile.
They made the point that the typical pattern of development for top strikers is to begin their careers with high shot volumes and for that to almost linearly decline as they get older, with the striker typically getting better quality shots to compensate. So normally you're looking for high shot volumes from a young striker as you know they will likely decrease over time.
Whereas the question mark over Hojlund is that he is currently the opposite of that, a low shot production, high-xG per shot striker. Which means we're essentially betting on his shot volume increasing as he ages, against the normal trend of it decreasing. And while there's nothing to say that can't happen, it means his development path is less predictable than it was for players like Haaland, Kane, etc. because it would be a lot less common. Added to that, Atalanta play an unusual system which requires the striker to behave slightly differently than they would in other teams, so anyone buying him would have to apply good subjective judgment in terms of how his skillset will translate to their team.
However against those two concerns, they thought the rest of his profile was positive as he's generally good at everything else. Passing, dribbling, getting on the ball, actually adding value in general play when on the ball, being a good progressive pass receiver (i.e. a focal point up front), etc. Plus his obvious athleticism.
Comparing him to other strikers, they noted that while his basic underlying stats weren't as impressive as someone like Ferguson's due to being a few years older, he offered a broader range of skills than Ferguson or Balogun. And if someone bought him for what Juve played for Vlahovic (€70m + €10) they'd be a lot more positive about it than they were about Vlahovic, because Vlahovic had a more limited profile and was older at the time.