In addition to jfb's recommendations for removing 1.1.1.1 from your router's DHCP DNS configuration, your ipconfig output shows your router's link-local IPv6 address.
This indicates that your router is advertising its own IPv6 address as DNS server, allowing your clients to by-pass Pi-hole via IPv6.
You'd have to find a way to configure your router to advertise your Pi-hole host machine's IPv6 as DNS server or to stop advertising its own.
You'd have to consult your router's documentation sources on further details for its IPv6 configuration options.
If your router doesn't support configuring IPv6 DNS, you could consider disabling IPv6 altogether.
If your router doesn't support that either, your clients will always be able to bypass Pi-hole via IPv6.