Wow, thanks for this tip. Saves the effort of having to manually find "all types" in the drop down... this is so much easier.

Also, just for clarification:

  Windows Registry Editor Version 5.00

  [HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Google\Chrome]
  "ExtensionManifestV2Availability"=dword:00000002

Apparently, the line Windows Registry Editor Version 5.00 is necessary at the beginning of the .reg file. This line indicates the format version for the registry file and tells Windows that it is compatible with the current registry editor (according to GPT). This worked for me.

Save the file as:

  EnableExtensionManifestV2.reg