Opening ports should be umbrel specific. Maybe ask in their support channels. It can be the case that they "automagically" open the right ports if you install pilhole through their app store.
You can check if the port is open and to other devices in your LAN by installing "nmap" on one of those other devices and running `nmap -p 53
If you can get a terminal session, you can try to figure out what do they use for firewall (ufw, iptables) and change it manually.