csrutil disable
Restart computer
In the terminal, type
sudo open /Applications/TextEdit.app /System/Library/LaunchDaemons/com.apple.ManagedClient.enroll.plist
change
<key>com.apple.ManagedClient.enroll</key>
<true/>
to
<key>com.apple.ManagedClient.enroll</key>
<false/>
So that the changes take effect
FWIW, I had the following FQDNs blocked at the router:
iprofiles.apple.com
mdmenrollment.apple.com
deviceenrollment.apple.com
gdmf.apple.com
acmdm.apple.com
albert.apple.com
I had them blocked in /etc/hosts as well. Still was able to update. Based on a quick search, gdmf.apple.com is specifically for MDM-managed devices.
Here is a list of all the FQDNs for the various services Apple devices might use
I have an unmanaged iMac and a used-to-be-managed Macbook Pro on my home network. My employer sends out alerts when there are major MacOS updates, critical updates, & patches. When the 14.4 notice came out, I went in to Software Update on both systems, and the 14.4 update showed up automagically as expected. No unblocking on my part.
If you truly do HAVE to unblock gdmf.apple.com to get updates, your machine may actually still be enrolled, but some other step in one of the techniques here suppresses the nag messages.
To check that, open Terminal and enter the following command:
profiles status -type enrollment
Your results should be :