File Encryption just for the content not for the file name.
We upload files to a partner and the partner that using a automatic process base on filename get the file form the server. For example we send the file customers_20190404.txt and their process look for a file called customers with today's date on the name.
File tha required to be encrypted the automatic process based on file names move it to the right department where it will be decrypted by the right person usin powershell or a custom code. But while is on the sftp server should be protected nobody not even IT department that has access to servers should be allowed to open the file.