@ServerCloud
The question is whether it makes sense at all to access SMB/CIFS across the Internet from a Nextcloud hosted on the Internet (IONOS). It is a SMB/CIFS client of the Nextcloud server and not the clients in the company. Perhaps you should consider whether this makes sense overall. I think the SMB/CIFS Nextcloud client makes more sense with on-prem Nextcloud installations in the same company network.