Modify page title

functions.php

<?php

add_filter( 'document_title_parts', function( $title ) {
    if ( get_query_var( 'explore_region' ) && ( $term = get_term_by( 'slug', sanitize_title( get_query_var( 'explore_region' ) ), 'region' ) ) ) {
        $title['title'] = $term->name;
    }

    return $title;
}, 99);

// Prevent conflict with YoastSEO
add_filter( 'pre_get_document_title', function( $title ) {
    return '';
}, 999, 1 );