Nope, I've never heard anyone say that DDLC is picked up by windows virus defender, nor do I even think its possible to itch.io games to be labeled as such.
I recommend installing Malwarebytes and running it to be sure. Windows virus protection is really bad, so I wouldn't trust it. You could have downloaded a virus on accident a while ago, and windows is only picking up on it now (since, y'know, it's terrible).