This topic has been discussed several times on the forum.
Long story short, the server automatically quarantined the game. Normally, it will be reviewed by someone on staff after a while.
If the person reviewing it confirms that there is nothing wrong (a false positive), the game will be removed from quarantine and everything will go back to normal.
What exactly triggers this? It has never been discussed publicly, to prevent bad actors from trying to take advantage. So there is not much we as developers can do except wait.
You can try to contact support and send any information that might help them, but you must contact support, as this forum is answered by the community and not by Itch support.
Edit:
Having the application signed does not guarantee anything, it can help prevent the Microsoft security window from appearing, but it does not guarantee that you will not trigger the Itch quarantine again.