His win over Carlsen wasn't considered to be superhuman. Neither player played perfectly. In his podcast, Fabiano Caruana (someone capable of judging this) said he felt very strongly that Niemann hadn't cheated in the tournament.

His ELO gains are impressive, but not unique. [1]

If he is cheating, no sensible hypothesis of how he's doing it has yet been offered. So it seems more probably he's a legitimately talented player whose merit's obscured by his past.

[1] https://twitter.com/ChessNumbers/status/1568340548490252288