Hi, I think there has been a misunderstanding.
It does not refer to the Dropbox Document Picker but to the iOS one. The bug occurs since iOS 13 when you use UIDocumentPickerViewController with UTTypeFolder, that is, to select a folder. But it is impossible to select anything in Dropbox, Google Drive, etc ... With other types for files such as UTTypePDF, UTTypeJPEG... access is allowed.
I know you can't do anything about it but if you could open a bug report in Apple maybe they will listen to you more.