To extend ManifestV2 in Chrome, add the text below to a text file, saving and running it as a .reg will create and add a value of 2 to "ExtensionManifestV2Availability" in the HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Google\Chrome key
(When you open/run a .reg file, it updates your registry, usually preceeded by a warning.)
Alternatively, you could do this manually by pressing the Windows key, type "run" (without the quotes) and enter, type "regedit" (without the quotes) and enter, then navigate as far as you can to HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Google\Chrome key
You may find there is no "Chrome" key and will need to create it, as well as creating ExtensionManifestV2Availability
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[HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Google\Chrome]
"ExtensionManifestV2Availability"=dword:00000002