Summary option in WordPress is not working.

Hello folks.
I am using this WordPress theme.

I can not set the articles to be with the Read More option.

When I am checking this option in: Settings > Reading > For each article in a feed show:

• Full text
• Summary

I just checked Summary and it is not working.

What should I do?
You can view my website here: https://imashon.com/

Thanks in advance!