AutoSave disabled when opening SharePoint-synced files from Finder after macOS Tahoe 26.6 update

Files stored in SharePoint Online and synchronized locally through OneDrive are opened as local documents when launched from Finder. Office applications display "Saved to my Mac" and AutoSave is turned off by default.

However, opening the exact same files through Word/Excel > Open > Sites, or via SharePoint "Open in Desktop App", correctly identifies them as cloud documents. In that scenario, AutoSave is enabled and collaboration/version history features work as expected.

Troubleshooting already performed:

• OneDrive reset and re-linked
• SharePoint library re-synced
• Signed out and back into both Office and OneDrive
• Removed Microsoft credentials from macOS Keychain and re-authenticated
• Recreated local OneDrive sync relationships
• Verified OneDrive File Provider extensions are enabled
• Verified Office applications and OneDrive are fully up to date
• Tested with newly created files and existing files
• Tested "Always Keep on This Device" with no change in behavior

The issue appears to be specific to the Finder-to-Office launch path after upgrading to macOS Tahoe 26.6.

Before upgrading to macOS Tahoe 26.6, opening the same SharePoint-synchronized files directly from Finder correctly preserved cloud document identity and AutoSave was enabled as expected.

I discussed this issue in detail with Apple Support, but they quickly dismissed it, saying that the problem is not on Apple's side and that I should contact Microsoft instead.