nnqxqzx Google Search Console "Sitemap Couldn't fetch" issue is temporary one from Google's end and you shouldn't worry about it. Just submit your sitemap and recheck Google Search Console after 2-3 days. You will find your sitemap has been picked up and processed.
Still, you can access robots.txt file in this directory: /var/www/example.com/htdocs/
If you don't find a robots.txt file in the above directory then it means your WP installation is using the default (dynamic) Robots Text file and you should create robots.txt file using SFTP and make sure it has right file permissions just like other files in htdocs directory.
