I'm trying to understand what conditional forwarding actually does and looking at the settings page, I don't understand what "these requests" is referring to:
The preceding paragraph mentions (names of) devices but no requests. So I'm guessing that requests refers to "requests from devices on my local network"? But what kind of requests? Since pihole is about DNS requests, it's probably about DNS requests. (But all DNS requests my pihole receives are (almost by definition) coming from local devices... But that's just an aside).
So if this is about DNS requests from my local devices, then I don't understand what the point is in forwarding those to the DHCP server on my router. What does a DHCP server do with a DNS request? So, apparently this is not about DNS requests? And even if my router does something with those requests, how will this magically change pihole tables such as Top Clients?