Hi there,
For some users simply restarting the computer fixed the issue. For some other users, opening and closing file explorer fixes the issue .
So it seems you have tried the methods as per this link https://social.technet.microsoft.com/wiki/contents/articles/33801.remote-desktop-troubleshooting-unable-to-copy-paste-files.aspx
Additionally try out these options and see if they are helpful
Use System 32 Folder
Reset the rdpclip.exe process
Use the “echo off” command on Command Prompt
Restart Windows explorer
Check individual applications
Disable the antivirus program temporarily
Hardware and devices troubleshooter
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