Yeah no problem. I've read that too, Microsoft even has a page on false positives. Windows Defender is trying to prevent the completion of the download from itch due to Defender believing it has encountered a Wacatac.B!ml trojan. I'm sure most of us do not use Defender normally but I just hadn't disabled it yet and thought that giving you a heads up would be nice since you never know what AV someone might choose to use. Not sure where exactly it thinks it finds it but I hope I might have helped a bit.
Update: Problem seems to be only with Windows Defender, other AVs find no threats.