I would not use Russian casinos. First of all, I think if I gamble on Russian casinos and lose, then at some point I indirectly support the Russia against the Ukraine because the profit that casino makes goes into Russians budget and funds their soldiers.
Look on a situation from different angle. Try not to lose, but instead make Russian gambling platform go bankrupt. With it, you will reduce amount of tax paid and reduce war funding. How do you like that ? Would you support the movement aimed to bankrupt Russian gabling platforms? Or lets hire Ocean and his friends to rob their safes?
You see, all these boycotts, sanctions, rallies, bans or leaving Russian market does not work so far. This situations between Russia and Ukraine must be settled on a different level.
I agree that the current sanctions are ridiculous. Russia should be completely cut off from trade with the world. Then Putin would definitely think very quickly about what was more profitable for him. I think about the sanctions that were once imposed on Iran.
However, if no one is doing it so far, then all boycots, even if they do not have a large impact on the Russian budget, are a clear signal that the world does not accept a pointless war.