New Mac iCloud sync stuck on "Waiting to Upload"

Hi,

I recently got a MacBook Pro 2020, updated to the latest Mac OS Big Sur.

I also have a MacBook Pro 2013, also running latest Mac OS.

Both Macs are logged into my same Apple ID. The old Mac is syncing iCloud Drive just fine.

However, my second Mac only syncs App Library folders (Pages, Numbers, etc), but not Documents and Desktop. They show in finder stuck on "Waiting to Upload" with the dashed cloud icons.

Any file I put inside those directories from the new Mac also stay uploading forever.

I already tried turning off and back on the "Desktop and Documents Folders" option in my Apple ID -> iCloud Drive setting, I've also tried logging out and back in my Apple ID.

Everything: Books, Photos, Notes, Reminders, syncs just fine except Documents and Desktop.

Thank you for any possible solutions or reasons that may be happening.