By itself, that failing test for LLA resolution isn't reason of concern, see DNS resolution on LLA address fails - #2 by Bucking_Horn.
Especially if you would configure your router (Freebox?) to not advertise any IPv6 addresses as local DNS server, exclusively using its IPv4's DHCP server for distributing Pi-hole's IPv4 address as your sole DNS server.
You'd have to consult your router's documentation sources on further details for its IPv6 configuration options.
But if your router would neither support disabling IPv6 RDNSS router advertisements nor setting a custom IPv6 address for DNS, your IPv6-capable clients will always be able to bypass Pi-hole via IPv6.
You could then try to mitigate this, by setting Pi-hole as the only upstream of your router, provided your router supports it.
But note that you won't be able to attribute DNS requests to original individual IPv6 clients in such a configuration.