This may be somewhat OT but possibly someone knows how to fix.
My Win11 laptop gets ipv4 and ipv6 DNS (the router) via DHCP just fine. Unfortunately, it also adds its own IPv6 as DNS resolver that then apparently goes somewhere else (MS or what have you, presumably not using regular DNS on port 53 as that one is hijacked by https-dns-proxy) and then fails to resolve local hosts. 
If I force the IP of the router in nslookup, it works like it should...
What is your IPv6 DNS setting or [DNS] announcement config IPv6?
Bog standard, no specific IPv6 setting anywhere (IPv6 works as far as I can tell)... The router's internal ipv6 makes it to the laptop's DNS config just fine but it also adds itself somehow.
You must have misunderstood me. I'm suggesting that you make the setting.
Browse to: Network > Interfaces > LAN > DHCP Server > IPv6 Settings:
Add the corresponding IPv6 servers here as well. Devices also use SLAAC in addition to DHCPv6 (although I'm confused if you never made such a specific setting, how you get them via DHCPv6, but no worries.)
Well maybe I get it through SLAAC; not sure. I have added the routers internal IPv6 to the announcement list, did not prevent Windows from doing it's own thing.
It works with static DNS, I guess could go to static DNS on Ethernet - at home that would be ok, everywhere else, on WiFi, let it do what it does.
How are you making the determination the Windows machine is receiving DNS from somewhere else?
Based on the fact that it resolves public DNS entries but not private ones unless I a) direct nslookup to the local DNS or b) set local DNS in the Windows settings as static DNS. It also shows its own ipv6 as resolver without static DNS
