"I found a solution to retrieve the data. My situation is that the blogger's situation is the same. 4T external USB mobile hard drive, APFS encryption is performed. Insert macbookpro cannot be loaded. mount prompt 4928 error at disk management point. First aid is also a mistake. My solution is to use Windows system. Connect to the 4T external mobile hard drive. Install the apfs from windows tool online. You can find the disk. Turn in the encryption password and you can see the files on the disk. But it can only be read but not written. Copy all the files inside. Then enter the macos system and use disk tools to format the file and copy the file in."