This is a great suggestion. I've run two on my local network for about five years:

pi#1) My personal DNS resolver, which I manually configure on each device.

pi#2) The much less restrictive DNS resolver which my DHCP server automatically issues to all other network clients, including all phones and IoT [0]

Individual hosts can then manually configure their DNS to resolve to the local network router (or third-party DNS), which effectively bypasses both PiHoles (for that device, only).

[0] There is a method to use a firewall to capture all outbound DNS and force routing through PiHole (ifsense? I don't know), which may be necessary for hard-coded DNS-IPs. I do not know how to do this but it's not necessary on my network.