How to set the server path of Google Drive
Welcome to the forum @He_Dong
At least for Google Drive Personal (not Business), you first decide where you want the backup.
Type that in with a minimum number of forward slashes, and let Duplicati do its folder creation.
You can use the Test connection button on the Destination screen to do this during setup.
Duplicati by default is access-limited (adds security) to folders and files that it created for itself.
Example Path on server would be Duplicati Backups/Computer 1, but set it as you wish.