Hi - I came on here to see if you had issues with select_advanced search on a post field.
I filter by taxonomy on mine (so need to change to meta_key / meta_value), but incase it is helpful for structure, I use this:
'query_args' => [
'post_status' => 'publish',
'tax_query' => [
[
'taxonomy' => 'institution-category',
'field' => 'term_id',
'terms' => $filterterms,
],
],
],