Someone in the steam comments says they joke a lot about pedophilia.

I think the only time this is brought up is someone falsely accusing Date of being a pedophile, but I don't remember the exact context of it.

Is it like the typical anime young girl fetishization stuff?

I don't recall anything like fetishizing underage characters, but there is plenty of pervy anime humor tbh. There is a character Iris who is an 18 yo streamer/idol and at least a couple of the characters are pervy simps towards her. There also is a subplot of an older rich guy dating a high schooler but it's not played for laughs and portrayed very negatively.

So I found this CW guide which is extremely detailed and probably contains everything objectionable: https://drainbangle.tumblr.com/post/655488958657085440/ai-the-somnium-files-content-warnings It's pretty thorough, though I do disagree a bit with the characterization here of how LGBTQ characters are treated.

I definitely would agree with that guide that there's a lot of "anime bullshit", so I would definitely steer clear if you want to avoid that kind of thing.

It's a visual novel with detective and puzzle elements.