How to duplicate a git repository on gitlab/github without forking?

In gitlab there is functionality out of the box:

1. Go to Settings -> General of existing project
2. Last expanded panel Advanced contains Export button. Click it and then on the top of this page you can see info message Project export started. A download link will be sent by email.
3. Check email. There is following message:

Project NAME_OF_YOUR_EXISTING_PROJECT was exported successfully.

The project export can be downloaded from: SOME_LINK The download link will expire in 24 hours.

1. Click SOME_LINK and then check the Downloads folder
2. Go to Project - Your projects page
3. Click the button New project
4. Set name of your new project on Blank project tab
5. Then go to Import project tab
6. Click the button Gitlab export
7. Click Choose file and select previously downloaded file *.tar.gz
8. Click the button Import project
9. Then you will see Import in progress label.
10. DEAL

source : https://stackoverflow.com/a/58525049