Hello @Nazarener,
Thanks for writing to us.
You are not able to set your “Permalink” as “Post name”.It’s not due to WordPress. The reason it’s not working is the webserver where WordPress is running is not properly configured for URL rewrite. It’s automatic on Apache’s “.htacess”, but not on NGINX server.
I found that your website is running under NGINX, which may require a different rewrite configuration. I would recommend you to please contact your hosting provider to set the WordPress rewrite configuration.
To learn more about how to configure Nginx for WordPress permalinks please have a look at the article. https://www.cyberciti.biz/faq/how-to-configure-nginx-for-wordpress-permalinks/
Thanks