Pico automatically cuts off text based on word count, and it inserts the Read More button. Right now, that's hardcoded (although may be adjustable in the future). You can override our placement of the Read More tag in the Wordpress admin by placing the Read More tag wherever you'd like.
In newer version of Wordpress, you may use the Read More block:
You can find more information on Wordpress here: https://wordpress.com/support/wordpress-editor/blocks/more-block/.