Just want to reply here my discoveries, to save people the hassle of attempting this to find out it does not work, there are two types of GRE tunnels, GRETAP and GRETUN, one supports layer 2 features such as broadcast/multicast and one does not, the PFSense implementation appears to use the later which does not support this feature, please see the following article to show the difference
https://developers.redhat.com/blog/2019/05/17/an-introduction-to-linux-virtual-interfaces-tunnels#:~:text=While%20GRE%20tunnels%20operate%20at,header%20in%20the%20inner%20header.
You would need a local UDP relay instead (on the client side) to instead allow the client to relay these broadcast message as unicast to a specific host, I struggled with this for Windows File Sharing (WS-Discovery) broadcast packets and ended up resorting to a script that auto maps all network drives on successful client connection, perhaps someone could get this working with a L2TP on top of Wireguard?
https://github.com/sparky3387/automapwireguard - Shameless plug of the automap script if someone else also needs this.........
