When you share a folder, you can exclude one or more subfolders from being shared. You just need to enter the subfolder names in the "Exclude folders/files" box. Multiple names can be separated by "|".
We just tested it and It works fine. Please note the subfolders must be the immediate subfolders of the share's root folder. For example, if you share a cloud folder: \SHAREROOT; in the folder, there are two subfolders: \SHAREROOT\SUB1 and \SHAREROOT\SUB2; in SUB1, there is a subfolder: \SHAREROOT\SUB1\NEST1, you can exclude SUB1 and/or SUB2, but you cannot just exclude NEST1.
Alternatively, you can move a subfolder to a different location. For example, you can move \SHAREROOT\SUB1 to \NOTSHARED\SUB1.
If you have more questions, please feel free to send an email to support.