Trying to solve my own matter, Outbound rule for youtube video suggests that I create enforced WAN1 outbound policy rules. The manual I have is for firmware 8.1.2 but I am on 8.1.3, so perhaps it is no surprise that I do not find outbound policy where the manual says. In Configuring Outbound Policy another user reports what I see, that under the top menu item “Advanced” there is no left menu entry “outbound policy”. I can get to the outbound policy pane by the direct URL https://192.168.50.1/cgi-bin/MANGA/index.cgi?mode=config&option=outboundpolicy but the pane is incomplete: there is no “add rule” button so cannot add an outbound policy, at least not here.
Am I barking up the wrong tree? Is there another way to ensure that YouTube is not available via the metered cellular service?
Additional information: I have a Surf Soho mk3. The unmetered ISP is connected to the Ethernet WAN port and is normally set to priority 1. The metered cellular service is connected to the USB port and is normally set to priority 2 in standby. Automatic failover is set up and works great.