This is a widespread windows problem. The executable isn't signed so windows refuse to accept it as legit. Problem is, the kind of certificate needed to sign the game are quite expensive and this is a free game.
The steam version might not have the issue if steam bypass the windows is it legit check. I would not look for a link outside of itch.io and steam. Everything else is much more likely to be a real virus.
There should be an option to ignorr the virus warning and download anyway