Hannity made up this term
https://www.cbsnews.com/news/what-is-the-alt-left-trump-was-talking-about/
So who uses the term "alt-left"?
It grew out of the conservative media. In particular, Fox News host Sean Hannity, an outspoken supporter of Mr. Trump, frequently references the alt-left on Twitter.
?ref_src=twsrc%5Etfw&ref_url=https%3A%2F%2Fwww.cbsnews.com%2Fnews%2Fwhat-is-the-alt-left-trump-was-talking-about%2F
?ref_src=twsrc%5Etfw&ref_url=https%3A%2F%2Fwww.cbsnews.com%2Fnews%2Fwhat-is-the-alt-left-trump-was-talking-about%2F
?ref_src=twsrc%5Etfw&ref_url=https%3A%2F%2Fwww.cbsnews.com%2Fnews%2Fwhat-is-the-alt-left-trump-was-talking-about%2F
In a November appearance on Hannity's show, former White House communications director Anthony Scaramucci said the alt-left think Trump voters "are misogynists and misanthropes and negative people."