itch.io

Many reasons can exist for the game to be flagged in some systems, since anti-virus use heuristic methods, which are not precise but statistical.

For example, since version 1.5, the game does an HTTP request to Itch to get the version of the current published game. That behaviour can be considered suspicious on many anti-virus.

Anyhow, in case of doubt, use VirusTotal and always run games on an sand-boxed environment, like Firejail (linux) or Sandboxie-Plus (windows), keep yourself safe :).