I remember that years ago it was 6 confirmations and then slowly people started to accept 3 confirmations and then some businesses, mostly casinos risked accepting transactions with 1 confirmation. I personally think that 3 confirmations is enough and 6 only delays the access to funds.
Crypto casinos can afford that luxury because they are in total control of the coins on their platform and you are just gambling with digits on a screen. Some casinos accept 0-confirmation transactions. You can play as soon as their system recognized the receiving transaction. It doesn't need to be confirmed. But if you get lucky and win, your deposit transaction has to confirm before you can withdraw your winnings. They can't lose their own money by accepting unconfirmed transactions. Only the players can lose.