macOS Monterey Beta 7 Working with AudioGod's current EFI!
The process is a little more involved than the Beta 6 upgrade but the following steps worked for me (as outlined by @AudioGod
in an alternate thread):
1. Copy your current EFI folder to a USB drive.
2. Open the config file in your current EFI folder (boot drive) and change Misc > Security > SecureBootModel to j160.
3. Open the config file in the EFI folder on the USB drive you just copied and change PlatformInfo > Generic > SystemProductName to iMac17,1.
4. (Re)boot off your current EFI folder. The update should now show up. Click Update Now.
5. While the update is downloading, open the config file in your current EFI folder and change Misc > Security > SecureBootModel back to Default (or Disabled).
6. Here's the tricky part. After the first reboot, override the default BIOS EFI option and boot off of the USB drive. Make sure the system selects the Macintosh HD volume.
7. After the second reboot, once again select your default BIOS EFI boot option. The system should select your Monterey volume and continue the install.
8. Bob's your uncle.