The Pi-hole team doesn't develop Apps for Umbrel, and Umbrel isn't on Pi-hole's list of supported OSs.
So far, we've only received reports for failing installs on Umbrel, see e.g. Pi-Hole in the Getumbrel node does not install, it always stays on.
Did your installation succeed?
If you can provide us with a debug token, I'll take a look and see if I can spot something.
To that end, please upload a debug log and post just the token URL that is generated after the log is uploaded by running the following command from the Pi-hole host terminal:
pihole -d
or do it through the Web interface:
Tools > Generate Debug Log