@Jake Lo one additional comment: in order to be able to install Monterey with the online installer, I needed to change one entry on the config.plist file:
Misc - Security - SecureBootModel was set to "Default" and needs to be changed to "Disabled".
Otherwise the pen drive boots into the recovery mode. When you click on "Install Monterey" it downloads all the needed files, but after the first reboot, something crashes instead of showing the Apple logo with the legend "XX minutes remaining".
Hope this helps.