new WP_Query to get max price meta value not working

As @Milo suggested and also codex documented it is_main_query Under_the_Hood

This function is an alias for the method WP_Query::is_main_query(). In
filter or action hook callbacks that are passed the WP_Query object,
such as pre_get_posts, it is circular to call this function.
Instead, directly call the passed object’s method. For example, if
your filter callback assigns the passed WP_Query object to $query, you
would call the method like so: $query->is_main_query()

You must change if conduction to 

function set_query_parameters($query) {
    if( !is_admin() &&  $query->is_main_query() && is_post_type_archive( 'properties' ) ) {
        $query->set('meta_key', '_featured_prop');
    }
}
add_action( 'pre_get_posts', 'set_query_parameters' );

There is no need to return the query. And I really wonder why you are not receiving a NOTICE because WordPress also trigger _doing_it_wrong() on using is_main_query() in this way!

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