Found at Creating files on GitHub | The GitHub Blog on 2022-05-19 15:41:53.

you can create new files directly on GitHub in any of your repositories.

This is the syntax of the “new file” URL that GitHub understands:

https://github.com/bpedro/public-notes/new/main?filename=/2022/05/19/20220519154200&value=Something%20to%20share.