From what I have seen, I think there are 2 processes as to how casinos accept crypto on their platform.
The first method involves providing users/clients with their own unique crypto address, which they can use to deposit funds using their preferred wallet to play the available games.
Alternatively, the second method involves integrating a payment processor like BTCPay
[1] into the platform. By doing so, the payment processor takes care of all the necessary steps concerning deposits and withdrawals.
This is just a guess based on observations and there could be some inaccuracies when it comes to process.
[1]
https://btcpayserver.org/