How do you distribute pihole's IP to the clients? DHCP or do you configure them manually?
If by DHCP: you have to dis/reconnect the clients from your network once to pickup the (new?) DHCP settings.
When I was using my Old router, pihole query logs were showing IP addresses of individual devices. Now it shows 192.168.0.1 (router's IP) only for all the queries.
Any reason why its behaving like that. And how can I change it to show assigned device's IP.
As you describe it, your router is distributing it's own IP as DNS server via DHCP to the clients.
From a quick search, you can't change the IP distributed as local DNS server to something else (you would want to distribute Pihole's IP).
Your'r only option seems to be to disable DHCP on your router and use Pihole as DHCP server if you want to see each individual client in the query log.