So I am have the fe80:: address from my pihole, as well as the 2601: address, and my router will accept the 2601: address as the ipv6 primary address, but it will not accept my fe80:: address as it is "Invalid format".
I have a Archer AX55 TPLink router, and am running pihole off a Pi 4, hooked up view ethernet. I am looking at the web interface under the network tab and have both the local and public ipv6 addresses of the pihole, and tried copy + pasting them in, but it doesn't appear to want to take my local address. Any ideas?
My guess would be that you are trying to configure your router for a public upstream DNS server, and your router assumes that only a public GUA IPv6 is sensible - or that you are simply mistyping the link-local address.
Try to locate the local IPv4 and IPv6 DNS options in your router and use those.
Your router's documentation and support channels should have further details on its DNS configuration options.