I sometimes play Crash on https://knifex.com/pages/crash. What I like is that it’s simple to use and the rounds are fast, so it’s easy to understand how the multiplier works.
If you’re just starting, my advice is to use small bets and cash out early until you get used to the pace of the game. Crash can be unpredictable, so it’s better to play carefully and not risk too much at once.