IANAL either, but my guess is that itch.io has precisely 0 plausible legal recourse here.

The strongest case would be something along the lines of breach of contract via the domain registrar, but your standard internet contract has a term in it that amounts to "we get the right to fuck you", so I assume that applies here, so no breach of contract actually exists. This also kills every claim that's dependent on breach of contract, so tortious interference is also dead.

Fraud will fail because itch.io itself isn't being defrauded at the very least. Business disparagement, and anything else along the lines of defamation, is going to fail because you need something like actual malice--specific knowledge of falsity--there, and that's essentially impossible to prove, not without somebody admitting that they knew all along everything was false.

Tortious interference is dead for several reasons. First, you need an underlying tort, which, as detailed above, probably doesn't exist. Next, you need specific knowledge of the contract being broken. Finally, you need intentionality here: it's not "I did something that caused the contract to be broken", it's "I did something to cause the contract to be broken." Outside of somebody jumping up and down shouting "I'm tortiously interfering with your contracts," it's basically impossible to prove tortious interference.