From your debug log - none of the assigned IPv6 addresses match the configured address for Pi-Hole:
[✓] IPv6 address(es) bound to the eth0 interface:
2a04:4540:6d06:db00:8a12:dd8e:fb02:5b00 does not match the IP found in /etc/pihole/setupVars.conf (https://discourse.pi-hole.net/t/use-ipv6-ula-addresses-for-pi-hole/2127)
2a04:4540:6d15:2600:8a12:dd8e:fb02:5b00 does not match the IP found in /etc/pihole/setupVars.conf (https://discourse.pi-hole.net/t/use-ipv6-ula-addresses-for-pi-hole/2127)
2a04:4540:6d15:2600:1cd0:827a:30c:cc89 does not match the IP found in /etc/pihole/setupVars.conf (https://discourse.pi-hole.net/t/use-ipv6-ula-addresses-for-pi-hole/2127)
2a04:4540:6d15:2600:2ffc:c821:14fa:92 does not match the IP found in /etc/pihole/setupVars.conf (https://discourse.pi-hole.net/t/use-ipv6-ula-addresses-for-pi-hole/2127)
fe80::8a12:dd8e:fb02:5b00 does not match the IP found in /etc/pihole/setupVars.conf (https://discourse.pi-hole.net/t/use-ipv6-ula-addresses-for-pi-hole/2127)
*** [ DIAGNOSING ]: Name resolution (IPv6) using a random blocked domain and a known ad-serving domain
[✓] instagramn.info is :: via localhost (::1)
[✗] Failed to resolve instagramn.info via Pi-hole (fd00::8a12:dd8e:fb02:5b00)
[✗] Failed to resolve doubleclick.com via a remote, public DNS server (2001:4860:4860::8888)
# A sample configuration for dhcpcd.
# See dhcpcd.conf(5) for details.
# Allow users of this group to interact with dhcpcd via the control socket.
#controlgroup wheel
# Inform the DHCP server of our hostname for DDNS.
hostname
# Use the hardware address of the interface for the Client ID.
#clientid
# or
# Use the same DUID + IAID as set in DHCPv6 for DHCPv4 ClientID as per RFC4361.
# Some non-RFC compliant DHCP servers do not reply with this set.
# In this case, comment out duid and enable clientid above.
duid
# Persist interface configuration when dhcpcd exits.
persistent
# Rapid commit support.
# Safe to enable by default because it requires the equivalent option set
# on the server to actually work.
option rapid_commit
# A list of options to request from the DHCP server.
option domain_name_servers, domain_name, domain_search, host_name
option classless_static_routes
# Most distributions have NTP support.
option ntp_servers
# Respect the network MTU. This is applied to DHCP routes.
option interface_mtu
# A ServerID is required by RFC2131.
require dhcp_server_identifier
# Generate Stable Private IPv6 Addresses instead of hardware based ones
slaac hardware
interface eth0
static ip_address=192.168.178.52/24
static routers=192.168.178.1
static domain_name_servers=127.0.0.1
Try dig @127.0.0.1 -p 5053 google.com AAAA as well to see if it returns the IPv6 addresses. You may not need IPv6 since and IPv4 resolver can hand out AAAA records just as easily as A records.
So just use 1.1.1.1 and 1.0.0.1 as the upstreams and take out the IPv6 ones. You'll get the same answers from IPv4 as IPv6 and save the headache of trying to get IPv6 right.
Then something is not configured correctly as the ipv6-test checks for IPv6 connectivity across the internet. And that test said you have no global internet IPv6.
Then back to the question I asked earlier, is cloudflared listening on IPv6?
The check on ipv6-test showing that the browser does not have IPv6 connectivity is telling that it doesn't matter if you have IPv6 AAAA records resolved, the client can't use them.
My suggestion is to just disable IPv6 on the router and forget about IPv6. You don't gain anything from having it enabled and it causes a lot of issues for people that are not well versed in networking.
