Currently the applause feature is being tested limitedly. The feature is “currently only available for purchase on computers. It’s also only available to viewers in Australia, Brazil, India, Japan, Korea, Mexico, New Zealand, and USA,” Google says.
It’s likely this feature will run into some controversy, as most of YouTube’s improvements do. If you’d rather just give your money directly to your creator, it’d be better to support them through their Patreon or other platforms allowing direct donations for now.