Results from the first dig tells that your client PC is not using Pi-hole for DNS resolution, but instead Google's DNS server 8.8.8.8 is answering:
Either on the router you find a setting called "DHCP server --> DNS" or similar and set the Pi-hole IP address to be pushed to the clients as their DNS server.
Or if that setting doesnt exist, disable the DHCP server on the router and enable the DHCP server on Pi-hole as a replacement:
And whenever changing DHCP settings, these changes need to propagate by either waiting untill the DHCP lease expires on the clients, or disconnect & reconnect network on the clients or reboot them.
And dont use a backup or secondary DNS server on the clients as the clients will query that DNS server too causing ads to leak through!