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Dear Robin.55,
Good day! Thank you for posting to Microsoft Community. We are happy to help you.
As per your description, it seems that you need more confirmation on sync in SharePoint and OneDrive.
If the understanding above is right, generally, clicking on "Sync" in SharePoint document site will create a new sync folder for the SharePoint site under the work/school account same with your Business OneDrive. You can check it by clicking on the blue OneDrive cloud in the notification bar > Settings > Settings.
If you choose to use "Add shortcut to my files" in SharePoint, the folder will appear under your OneDrive for Business directly as described in below official article.
For your reference: Sync SharePoint and Teams files with your computer - Microsoft Support
Sync SharePoint files and folders - Microsoft Support
We hope the above can help. If the understanding above is not consistent with yours or any further assistance needed, please feel free to post back and point that.
Your understanding and patience will be highly appreciated. We hope that you are keeping safe and well!
Thanks for your cooperation.
Sincerely,
Rhoda | Microsoft Community Moderator