Within PeepSo fields it's only possible to enable single select lists as
searchable. The following code uses PeepSo filters to allow you to include multi-select fields in the members search area by converting them to single select and including the selected value in the database query.
peepso-search-member-profiles.php file in /wp-content/mu-plugins with the following code:
<?php /** * Find the field IDs under PeepSo Manage Fields * Add the field IDs of multiple select fields you want to show for member search