True as far as I know that nobody has direct proof of him cheating in person (over the board / OTB). But he was cheating on a regular basis until two years ago when he was essentially banned from any online cash tournaments due to being identified as a cheater, including cheating against top players and in cash tournaments. He then took his grift to over the board chess where he has had an astronomical rise in rating including playing matches with a concordance to the engine on a regular basis which exceeds anything seen with top super-GMs.
Then when the controversy started at the Sinquefield Cup he delivered an impassioned defense admitting to cheating twice when he was much younger in online play, but lying about cheating more recently online and lying about cheating in cash tournaments. His coach is a known cheater who has been banned from any online cash tournaments due to being caught cheating.
So the defense that he hasn't been caught yet doesn't mean that he hasn't been cheating.... Also the match against Magnus Carlsen wasn't necessarily one of the more suspicious ones; his play took a huge dive in that tournament in the aftermath of his match and instituting a 15 minute delay on broadcasting, but could have other explanations (small sample size, stress of being spotlighted and implied that he was cheating).