generate excerpt from the part of big text dump that contains keyword

Question

I'm working on an older site with a million plugins that just can't handle SearchWP and trying to mimic some of that plugins functionality.

Things that ARE working:

1. my search includes an ACF textarea field with a big chunk of content client's drop in it (a transcript)
2. I'm able to create an excerpt from that ACF textarea field for search results
3. I'm able to highlight the keyword in the search results

What's NOT working:

I'd like a way to output the part of the full contents of ACF textarea field that contains the keyword. Right now the excerpt is being created with wp_trim_wordsbut always starts at the beginning. The highlighted keyword is snagged with the following code I found in another similar question on here:

$raw_content = get_field('transcript');
$trimmed_content = wp_trim_words($raw_content);
$keys = implode('|', explode(' ', get_search_query()));
$raw_content = preg_replace('/(' . $keys .')/iu', '<strong class="search-highlight">\0</strong>', $raw_content);

I don't have a preference for php or js.