I can see centralized mixers being subjected to some kind of KYC regulations. There have been instances of mixers being used to obfuscate the trail of stolen coins, but such instances are very few, Chainalysis has some data on that: https://bitcoinmagazine.com/articles/chainalysis-most-mixed-bitcoin-not-used-for-illicit-purposes.

Regarding decentralized mixers, Wasabi and Samurai wallets have something along those lines - this article might help shed some light on it - https://medium.com/cobo-vault/bitcoin-mixing-a-brief-research-into-centralized-vs-decentralized-390ea83fa6ad