

I have a multi-WAN configuration on my router, with ipv6 VDSL then ipv4 VDSL then a prepaid 4G modem as the backup link. I rarely fail over but it’s been fantastic watching traffic stats when it does.
My only downside is the CGNAT on that connection that prevents things like a backup VPN gateway…
BareOS is a great open source option. The GUI is a webUI but you also have a powerful console on the shell if you need to script.