Nginx configuration for Kirby A) in domain's root directory (e.g. example.com) B) in subdirectory named /kirbycms/ (e.g. example.com/kirbycms/).

kirby-subdir.nginxconf

# e.g. for example.com/kirbycms/
location /kirbycms/ {
    if (!-e $request_filename) {
        rewrite ^/kirbycms/(.*)$ /kirbycms/index.php last;
        break;
    }
}

kirby.nginxconf

# e.g. for example.com
location / {
    if (!-e $request_filename) {
        rewrite ^/(.*)$ /index.php last;
        break;
    }
}