Is it a prank, or a leftist tool to harm the right?
It started as a prank.
It surprises me that I seem to be the only one on this thread who understands that this is all the result of a 4chan hoax.
4chan is conservative. Its members are wizards of the internet. Operation O-KKK was one of their hoax masterpieces, though it may have evolved in a way they did not intend.
This piece by the Anti-Defamation League provides a good explanation.
https://www.adl.org/blog/how-the-ok-symbol-became-a-popular-trolling-gesture