Damaged external hard drives, corrupted files, outdated macOS, virus attacks, and malware infection, could be the reasons for the Finder error code 36.
When you try to copy, or transfer files from, or to an external hard drive, USB flash drive, or SD card, and receive the Finder error code 36, you can read this post to apply the following solutions:
- Disconnect the external hard drive, restart the Mac, and reconnect it
- Install an antivirus program and remove the virus on the Mac
- Run the dot_clean command in Terminal
- Log in as an admin and change files/folders permission on Mac
- Run First Aid in Disk Utility to check and repair disk errors
- Update macOS
- Delete the .DS_Store files