You do not have a DNS leak.
There is no leak if you are not using a VPN service.
Whatever page your are looking at - it just reflects what public DNS server your network has been using, as triggered by that test page.
If that is unexpectedly deviating for your Win11 client, that may hint at a client-specific by-pass of your network's DNS resolvers.
We've eliminated the DNS by-pass your router allowed via 1.1.1.1.
(Note that your leak test did not (and could not) reveal that - your debug log's Discovering active DHCP servers section did that.)
If DNS requests of your Win11 do not end up at one of Cloudflare's IPs, then some software your client is not respecting DNS resolvers as distributed by your router.
A likely such candidate would be a browser using DNS-over-HTTPS.
Make sure the browser you are using does not have has DoH enabled.
If none of your Win11 browsers is using DoH, let's check whether DNS requests would make it to Pi-hole.
Run from your offending Win11 client, what's the output of the following commands:
nslookup pi.hole
nslookup flurry.com
When executing those requests, closely watch Tools | Tail pihole.log:
Do both of these requests shop up?