Thanks for the screenshot.
Now, that reveals that you are using pihole as a name.
pihole is not a name that Pi-hole creates - it's entirely up to you to correctly set up resolution for that name.
A default Pi-hole installation will create the appropriate definitions to make its web UI available at http://pi.hole/admin:
When it comes to DNS resolution of the machine that hosts your Pi-hole, you have a choice of making use of Pi-hole or some public DNS, see Correct Resolv.conf entry in pihole 5.11.