I do not run bit defender, but can you disable it while you are checking. Since you are working on your LAN, you do not need the internet connection to be active if you are worried about it.
What did the troubleshooter say? Homegroups need IPv6 to work, perhaps yours is turned off or the router or firewall is not allowing that.
It has been my experience that Homegroups are very easy to set up, but the computers have to see each other.