I want to see how the casino works first. Preferably with a registration bonus - free spins, maybe a free balance. I don't want to invest money right away. Are there such options now?

Sure, try PinUp casino. They periodically have promotions with no deposit bonuses - for example, free spins for registration. I personally received 25 free spins on a slot just by confirming my email. This is a great way to get to know the platform, interface and assortment. Even if you don't win anything, you'll understand whether you like playing here at all. And if you're lucky, you can start without investing.