Syntoy 2.1 doesn't decrypt encrypted files and folders whereas Synctoy 2.0 won't copy file attributes such as for encryption.
When using version 2.0 all my encrypted files and folders are decrypted.
This occurs when copying between two NTFS formatted drives. If copying between an NTFS and FAT drive encryption and NTFS file attributes should be automatically removed.
I'm uncertain about ver. 1.4. Previous download links are broken and MS replaced the 1.4 download link with version 2.0.
If you have many encrypted files to copy to a removable drive, you don't necessarily want backup files and folders to be encrypted when attached to other PCs.
I remember Synctoy 2.1 being somewhat faster than ver. 2.0 but haven't actually performed any testing, 2.1 seems to be faster.
I have both 2.0 and 2.1 (x64) installed. Perhaps MS should have added some sort of option(s), but wanted to keep Synctoy simple as possible.
If you have many encrypted files that need to be decrypted. When using ver. 2.1 you would need to add additional time for decrypting hundreds to thousands of files vs the amount of time it takes version 2.0.