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
Updated to 14.3.1, works for me, remove gdmf.apple.com from hosts before updating(in another way it wouldn't find updates). After updating finished, back it to hosts. Nothing special is needed if you are on 14.1.* - 14.2.* you can update your OS via UI (Software Update).