WAN cannot be set to "track". Your internal interfaces track the WAN.
Multi-WAN is quite complicated. Multi-WAN with IPv6 is even more complicated. Did your TP-Link/Omada setup support it?In your earlier posts, you weren't even sure if your ISPs provide IPv6 at all. I'd suggest getting it working with one ISP first (or maybe you have, and I missed it?), then the other ISP, then worry about multi-WAN.