Empty files after first iCloud sign-in

Dear Community,

few days ago, iCloud asked my father to log-in in his macbook air.

His macbook has never been logged to iCloud.

After he logged, all files from local/Desktop were moved to iCloud/Desktop. But something strange happened.

All .docx files were 0kb in size and became empty.

All PDF disappeared, as they were deleted. My father asked for my help.

If I explore the folder iCloud/Desktop through terminal app (command ls), i find all the pdf and they can be open.

I noticed that the iCloud warned that no storage was left. So I paid to extend my father storage. But the situation still remains the same.

What could have happened? How can I restore the situation before my father logged?

Regards and thank you for your help