When I use a Windows 10 PC, that makes DNS requests in IPv6, the used DNS server is my ISP router and not the Raspberry. IPv4 requests (for example from my Android smartphone and tablet) are correctly resolved by Pi-Hole. I have enabled the IPv6 setting during the Pi-hole installation and also from the panel, but it didn't worked. I'm also using the Raspberry as DHCP server and all the Windows PC's in my network use it correctly.
If I disable the IPv6 option from the network interface on Windows, the used DNS server is Pi-hole.
Can you please suggest me how to fix this? I found an option on my router that allows to forward all the IPv6 traffic to a specific device within a private LAN, can it be helpful?
Your router may be still sending out IPv6 packets with the wrong DNS information. Try seeing if there's a setting in there to turn off IPv6 advertisements. What is the label on the option you mentioned?
I can't even figure out what they exactly do... Reading the manual of the router it seems that leaving empty the rules of the second image all the traffic is forwarded.
And is it correct to have this value empty in the Pi-hole panel?
I don't have IPv6 connectivity and I neither see IPv6 queries in the log... The only thing I noticed using nslookup in the cmd is that if I disable the IPv6 connection the PC uses Pi-hole as DNS server, while with IPv6 enabled it uses the router.
