Pico automatically cuts off text based on word count and it inserts the Read More button. Right now that feature is hard coded and CANNOT be change.
If you are using the Pico Plugin for WordPress, you can override our placement of the Read More tag in the WordPress admin by placing the WordPress 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/.