The fun thing is Knock Off kind of got another nerf in gen 8 in official competitions.It's funny cause gen 7 sorta neutered Knock Off due to Z crystals and Mega stones not being knockoffable.
However those are gone in gen 8 so Knock Off is as powerful as it can be (moreso with how impactful heavy duty boots are nowadays)
The only ""competition"" on KnockOff in gen 8 is that it sorta competes with Poltergeist, however as far as I know for now the users of Poltergeist that are viable in any given tier are usually 1 or less (maybe for the better considering one of few things keeping certain ghost types in check is the lack of a strong physical stab)
Smogon, and random battles, just uses anyone. Official Competitions have to deal with Mark restrictions and that meaaaaaaanssssssssss
https://bulbapedia.bulbagarden.net/wiki/Knock_Off_(move)
It's not a TR, so a bunch of Pokemon lost access to the move entirely. Much like Toxic, this seems very intentional, especially combined with the pokemon who now learn it naturally.