Casinos usually give announce by showing a window box when users log in to their account. I have seen this in some casinos so that will attract attention from users to check it out which one has changed. They will understand the changes on the terms and conditions because casinos need to update following the regulation.
Yes, that should make a big panic or noisy in their members if they announce the change. The other ways the casinos can do is send an email related to the change so their members will know and understand and now that will depend on them still stay on the casinos or move to the other casinos.
Different companies have different approaches on how they inform their users about changes in ToS. Update channels can be on their platforms with a pop-up announcement, through email notification, on social media channels like Telegram, Discord, X, Facebook and more. Some platforms have their Change Log pages for noting down important changes on their platforms.
As said, companies have diversifying approaches and there is no standard on how a company should or must do it. Personally, more transparency in big policy changes should be better and it also shows how a company respects their users and treat them fairly enough.