I can copy full path of file:

{ "keys": ["super+i"], "command": "copy_file_path" }

But don't know how to copy its relative path (relative to project folder)

I even created .sublime-project

{
    "folders":
    [
        {
            "path": ".",
            "folder_exclude_patterns": ["node_modules"],
            "follow_symlinks": true
        }
    ]
}

But copy_file_path still copies absolute path.