FOLDERS don't have a read-only attribute in Windows. The read-only attribute is only for files within the folder. The read-only check-box for folder properties is a bad design default. Windows file systems actually use the read-only attribute for a folder to make it, supposedly to make it fully customisable, but the checkbox in a folder's properties has nothing to do with that. In fact, you cannot stop a folder's contents from being changed using the read-only attribute.
Unfortunately, some software does not interpret this correctly. I use Ashampoo, for example, which sees my default save folder as locked with the read only attributte