A group of Microsoft Products and technologies used for sharing and managing content, knowledge, and applications.
Hi David,
Firstly you can configure which client starts when users click the Sync button in a SharePoint document library.
Please browse to the SharePoint admin center as a admin:
https://contoso-admin.sharepoint.com/_layouts/15/online/TenantSettings.aspx
Under Sync Client for SharePoint > Set to "Start the new client".
Or, you can just launch the new client (OneDrive.exe) located at %LOCALAPPDATA%\Microsoft\OneDrive, add your account to start syncing.
Additionally, you can configure your new OneDrive app to sync SharePoint library files by setting registry keys. Please check this article:
Enable users to sync SharePoint files with the new OneDrive sync client
Regards,
Jim