Custom Hook BEFORE First H2 Heading (Affiliate Disclaimer)

What's the easiest way to insert my affiliate disclaimer (made in GP Elements) before the first H2?

I've tried a bunch of different approaches, including tweaking some of the other custom hooks mentioned in other threads. All the other threads are for hooking after the H2 (I usually have images there already).

This is basically the code I've been tweaking:

add_filter( 'the_content', 'insert_content_after_paragraphs', 20 );
function insert_content_after_paragraphs( $content ) {
    $html = do_shortcode( '[your-shortcode]' );
    if ( is_single() && ! is_admin() ) {
        return prefix_insert_after_paragraph( $html, 1, $content );
    }
    return $content;
}
// Parent Function that makes the magic happen
function prefix_insert_after_paragraph( $insertion, $paragraph_id, $content ) {
    $closing_p = '</h2>';
    $paragraphs = explode( $closing_p, $content );
    foreach ($paragraphs as $index => $paragraph) {
        if ( trim( $paragraph ) ) {
            $paragraphs[$index] .= $closing_p;
        }
        if ( $paragraph_id == $index + 1 ) {
            $paragraphs[$index] .= $insertion;
        }
    }
    return implode( '', $paragraphs );
}

The code mentioned here for some reason puts the block at the bottom of my post. This one seemed useful, but I couldn't get it to work either.

It's difficult because my intro is sometimes 1 paragraph, sometimes 10, so I cannot use the after N paragraphs approach. Recently, I've put different sections of the posts in containers (so the first H2 is sometimes inside a container). I tried Ad Inserter, and had no problem with ads, but couldn't figure out how to insert a GP element specifically.

Thank you!