Hi there,
GP 3.0 introduced the generate_do_template_part()
function.
It can be used in a variety of ways, such as replacing the loop content template.
It also has its own hooks, heres an example of that for adding content within the archive loop ( eg. insert content after X posts ):
https://docs.generatepress.com/article/generate_after_do_template_part/
However, what it does not do is filter the_content()
which is what you require if you wanted to insert content after X paragraphs. Heres an example of that:
https://generatepress.com/forums/topic/insert-html-element-above-first-h2-in-single-posts/#post-873244