Hi,
There are several Group Policy you can try to check if they will help you:
Prevent users from syncing libraries and folders shared from other organizations: https://learn.microsoft.com/en-us/sharepoint/use-group-policy#prevent-users-from-syncing-libraries-and-folders-shared-from-other-organizations
Prevent users from syncing lists shared from other organizations: https://learn.microsoft.com/en-us/sharepoint/lists-sync-policies#prevent-users-from-syncing-lists-shared-from-other-organizations
Block syncing OneDrive accounts for specific organizations: https://learn.microsoft.com/en-us/sharepoint/use-group-policy#block-syncing-onedrive-accounts-for-specific-organizations
Allow syncing OneDrive accounts for only specific organizations: https://learn.microsoft.com/en-us/sharepoint/use-group-policy#allow-syncing-onedrive-accounts-for-only-specific-organizations
Prevent users from changing the location of their OneDrive folder: https://learn.microsoft.com/en-us/sharepoint/use-group-policy#prevent-users-from-changing-the-location-of-their-onedrive-folder
Prevent users from syncing personal OneDrive accounts: https://learn.microsoft.com/en-us/sharepoint/use-group-policy#prevent-users-from-syncing-personal-onedrive-accounts
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