Hello,

Hoping for some guidance on the best way to solve my problem.

I'm using a wireguard tunnel for connectivity to another site with multiple services running over this. Primarily using a wired internet connection, with failover to LTE if there is an issue. This is already working.
I'm running video traffic over this tunnel, but want to block Video traffic (RTSP 554) ONLY if the wireguard tunnel is online over the LTE connection.

i.e.
Wireguard comes up via ethernet interface, allow video traffic
Wireguard comes up via LTE interface, block video traffic

Hopefully I've explained this well enough.
Ideas?

NOpe not a clue, try a diagram.
Are both sites MT,
which site is server and which client for initial handshake?

Sounds like you have two wg tunnels, one for one WAN, and one for the other.
Thus it should be easy to use firewalls at either end to stop such traffic cold by port#