Really weird, the game is completely open source so it being flagged by an anti-virus is unlikely. Never heard anything like this before in the community.
Regardless, you can play the game by installing Java from here: https://adoptium.net/temurin/releases/ (Choose any JRE with Java 8 or above)
Restart your System.
and then download the JAR file for the game from here: https://github.com/yairm210/Unciv/releases/latest
And then double clicking the JAR file will start the game.