To @OP
The question should not be which exchanges have been hacked but which exchanges have never been hacked. =)
Here are 4 exchanges that have never been hacked:
Phemex
Bybit Crypto Exchange
PrimeXBT
Kraken Crypto Exchange
https://crypto.news/top-crypto-exchanges-that-have-never-been-hacked/It's just a matter of time until we hear they get hack, so no exchange is safe