Hello @Ano Acco
They are often used interchangeably. BYOK usually means the vendor holds the key, but you create it and upload it. CMK can mean that but also sometimes reflects the case where you hold your key in your own KMS instead, so it tends to encompass more patterns than BYOK does in practice
In more detail:
https://www.cryptomathic.com/news-events/blog/what-is-the-difference-between-byok-cyok-hyok
I hope this helps!
Kindly mark the answer as Accepted and Upvote in case it helped!
Regards