Stop Outlook (new) Signature Sync / Roaming Signatures

Hi,

We're running into the problem that our Outlook (new) keeps syncing signatures on a mailbox that is being used by multiple people. I would like to stop/prevent roamign signatures or the signature sync so that the users can add their own name in the signature.

I'm unable to add the DisableRoamingSignaturesTemporaryToggle registry key in HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\Setup\ since we're using the new Outlook from the old default mail app. We do not have the Office apps installed and we're using a gmail account.