He has an entire video about cleaning keyboards that consists of putting them in the dishwasher as a whole, PCB included. There’s no way that’s ever a good idea because of corrosion.

This seems to be in agreement with what I said, but you appear to have put it up as a counterexample. Showman means entertainment. He's an entertainer. He also seems to be one of the rare entertainers who doesn't fib for greater entertainment value. The LTT labs thing linked elsewhere suggests he cares about the technical side and, like BuzzFeed News, wants to use entertainment to fund more serious stuff.

I don't see a problem here. The keyboard thing sounds entertaining, so I'll go check it out.

Yet the video shower that wasn't an issue and he gave tips how to minimise corrosion anyway

They later on, as a side part of a last year or so video, discussed that all pf those keyboards failed a few months afterwards. The cause was not discussed but I would guess washing introduced either corrosion and/ or a lot of wear tp the keyboards. They mentioned that they would like to revisit the concept later but, iirc, it hasn't been done yet.