There is no “official” way to enable Intrusion Detection Sync Firewall following a sysadmin module upgrade if the option was not enabled prior to updating the module.
Before the update, the link in System Admin for Intrusion Detection would point to this page: /admin/config.php?display=sysadmin&view=intrusion_detection
As you can see, there is a gear that we can click on to activate the following dialog:
After the update, the link in System Admin for Intrusion Detection now points to this page: /admin/config.php?display=firewall&page=about&tab=intrusion_detection
So unless someone knows the URL for that previous page, there is no way to enable the Intrusion Detection Sync Firewall after an update. Confirmed with syadmin module version 126.96.36.199.