Sliders of any kind on a mobile device can be troublesome. iOS uses swipes for numerous gestures such as opening the control center.
I followed a link from my iPhone email and so Medium opened up in Chrome. Swiping the clap icon left to remove claps would almost certainly lead to people accidentally going back to the previous page in their browsers.
The best solution IMO is to tap once for a single clap, hold to reveal “5, 10, 15, 30, 50” similar to how Facebook works with reactions.
The clap would then show a badge indicating the chosen number of claps. If the user wants to change their clap amount they simply hold and change.