Hi three, there are a few options for you. The first is to insert the More Tag in your posts. That would affect the blog, tag, category and date archive pages, not just the category pages.
Second would be to try the Easy Custom Auto Excerpt plugin. I’ve not used this plugin, so I can’t make a recommendation one way or the other. The only possible problem I see from their description is that they mention it working if the theme calls the_content and Revelar calls the_post so I’m not sure if it will work.
The third option would require the creation of a Child Theme and then you would need to copy over the archive.php file from the original theme to the Child Theme and then modify the post loop to use Excerpts instead of the full text of the post. If you wanted to show excerpts only on category pages, they the PHP scripting change to this file would get a bit more complex.
The excerpt function reference: https://codex.www.ads-software.com/Function_Reference/get_the_excerpt
