Upgrade from NC18 with ZimbraDrive user

I would like to upgrade my current installation NC18 to NC19 better to NC20/NC21.

In the NC18 installation, users were created by Zimbra/ZimbraDrive in the table oc_zimbradrive_users.

Don’t use the app anymore and switched to Barry’s solution with WebDav but the authentication still runs through the backend:
‘user_backends’ =>
array (
0 =>
array (
‘class’ => ‘OCA\ZimbraDrive\Auth\ZimbraUsersBackend’,
‘arguments’ =>
array (
Would therefore like to ensure that before updating to NC19 … users can still log in after the update. In NC19 the backend (Zimbra Drive) is no longer available.

Hence my question, if I upgrade from NC18 to NC19 … , can the users still log in?

If no, what alternatives are available? Can I just set each user the same password again and then they can log in?

What are the alternatives here?

Thank you very much!