@PaintTheNight, couple of steps. First make sure Load Balancing is disabled, make sure your primary uplink to WAN1, then set Internet Flow Preferences that match the source IP address(es) of your internal subnets and a destination of Any to use WAN2. Since the primary uplink is set to WAN1 this will be used as a preference, but all internet bound traffic that matches the Internet Flow Preferences will be routed over WAN2.
You could also approach this the other way round too. Set the primary uplink to WAN2, and then set a SD-WAN policy for VPN traffic with a filter of Any protocol, Any source, and Any destination to use WAN1 and failover if the uplink is down. This way the internet traffic will follow the primary uplink (i.e. WAN2) and the SD-WAN/VPN traffic will follow the policy you define.
Either way should work.