Numbers and Excel files open slowly only in shared iCloud Drive folders (works fine with Dropbox)

I’m experiencing a consistent delay when opening spreadsheet files (both Apple Numbers and Excel files) stored in a shared iCloud Drive folder. The same files open instantly when located in a non-shared iCloud folder or when shared via Dropbox with the same collaborator.

Here’s the situation:

• The shared folder is inside my Documents folder, which syncs with iCloud Drive.
• Optimize Mac Storage is turned off, and all files show the green checkmark (fully downloaded locally).
• Files open immediately when I move them outside of the shared iCloud folder.
• Once shared with another Apple ID, opening a file shows a long “Opening…” progress bar in Numbers or Excel, even though the file hasn’t changed.
• The same folder copied to Dropbox and shared with the same user works perfectly — no lag at all.
• Bandwidth is not an issue — both my location and the other user’s location have 1 Gbps upload and download speeds, confirmed by speed tests.

From my testing, it looks like iCloud adds an extra “collaboration check” each time a file in a shared folder is opened, even when it’s already local.

Has anyone else seen this latency in shared iCloud folders, and is there a workaround or improvement in macOS Tahoe for this behavior?

Thank you in advance for your help and insights!