How to get the last date updated of postmeta?

No WordPress does not track that information. You can’t find it because it does not exist. Unless you specifically wrote code to track when post meta was added/modified, that information doesn’t exist, and it’s rare that any plugin would implement this as it would result in a lot of data collection. It would also be … Read more

Query a meta key using an array of values where the database value is a string

You could use multiple meta clauses in your WP_User_Query, along with a LIKE comparison. Something like $args = array( ‘role’ => ‘member’, ‘meta_query’ => array( ‘relation’ => ‘OR’, array( ‘key’ => ‘specializations’, ‘value’ => ‘doctor’, ‘compare’ => ‘LIKE’, ), array( ‘key’ => ‘specializations’, ‘value’ => ‘researcher’, ‘compare’ => ‘LIKE’, ), ), ); $found_users = new … Read more