Well multicast discovery isn't going to work vlan to vlan either.. And no L2 discovery doesn't work over vpn either.
I would check that you can talk to your device from lan to say opt 1 network locally, before you look to it working via a vpn..
I fired up the client on my phone.. On different wifi vlan then the vlan my camera is on... I then set it up to using IP..
works.png
There you go working just fine..
edit: I don't have wireguard installed, but just disconnected my phone from wifi, only on cell - connected to my vpn connection on pfsense openvpn... Bam - watching video stream from my phone.
edit2: possible problem with some camera's is if they do not have gateway set, ie pointing of pfsense - then you can not view them from other networks, be it a vlan or vpn. Without doing source natting.