Hello Yasmin,
Thank you for the clarification.
I had deleted iCloud, and changed to Google Drive, then I tried to add a file from Google drive to a specific folder in Boxcryptor, but again unfortunately the folder remains empty, nothing was transferred to, although the app asked me if I want to Encrypt the file, I clicked yes but nothing was transferred.
(I think) the issue is related to a permission that Boxcryptor is not gained, and maybe if this is the case, and since you are a developer for Boxcryptor, you will need to contact Apple to find a fix in order for Boxcryptor to be compatible with iOS 13.
Best regards.
George