This code adds custom filters to the member directory of the Ultimate Member plugin. These filters are grouped - one filter searches in multiple fields.

um_grouped_filters.php

<?php

/**
 * Add custom grouped filters to the member directory.
 *
 * Add filters you need to this array. Every filter is an array where:
 *  - key    Filter key. Any valid string key.
 *  - type   Filter type. Accepts: 'text', 'select', 'slider', 'datepicker', 'timepicker'.
 *  - label  Filter label (used as the filter placeholder).
 *  - fields An array of usermeta keys. Filter searches a value in these usermeta.
 */
$um_custom_filters = array(
	array(
		'key'    => 'make',
		'type'   => 'text',
		'label'  => __( 'Make', 'ultimate-member' ),
		'fields' => array(
			'make1',
			'make2',
			'make3',
		),
	),
	array(
		'key'    => 'model',
		'type'   => 'text',
		'label'  => __( 'Model', 'ultimate-member' ),
		'fields' => array(
			'model1',
			'model2',
			'model3',
		),
	),
	array(
		'key'    => 'year',
		'type'   => 'text',
		'label'  => __( 'Year', 'ultimate-member' ),
		'fields' => array(
			'year1',
			'year2',
			'year3',
		),
	),
);

global $um_custom_filters;

// Add ustom filter fields.
add_filter( 'um_members_directory_filter_fields', function( $filter_fields ) {
	global $um_custom_filters;
	foreach( $um_custom_filters as $f ) {
		$filter_fields[ $f['key'] ] = $f['label'];
	}
	return $filter_fields;
} );

// Add custom filter types.
add_filter( 'um_members_directory_filter_types', function( $filter_types ) {
	global $um_custom_filters;
	foreach( $um_custom_filters as $f ) {
		$filter_types[ $f['key'] ] = $f['type'];
	}
	return $filter_types;
} );

// Add custom filters.
add_filter( 'um_frontend_member_search_filters', function( $search_filters ) {
	global $um_custom_filters;
	foreach( $um_custom_filters as $f ) {
		$search_filters[] = $f['key'];
	}
	return $search_filters;
} );

// Add custom filter labels.
add_filter( 'um_search_fields', function( $attrs, $field_key ) {
	global $um_custom_filters;
	foreach( $um_custom_filters as $f ) {
		if ( $f['key'] === $field_key ) {
			$attrs['label'] = $f['label'];
		}
	}
	return $attrs;
}, 10, 2 );

// Modify the um_get_members query (default usermeta table).
add_filter( 'um_prepare_user_query_args', function( $query_args, $directory_data ) {
	global $um_custom_filters;
	foreach( $um_custom_filters as $f ) {
		if ( ! empty( $_POST[ $f['key'] ] ) && ! empty( $f['fields'] ) ) {
			$value = sanitize_text_field( $_POST[ $f['key'] ] );

			$filter_query = array(
				'relation' => 'OR',
			);

			foreach ( $f['fields'] as $field ) {
				$filter_query[] = array(
					'key'     => $field,
					'value'   => $value,
					'compare' => 'LIKE',
				);
			}

			$query_args['meta_query'][] = $filter_query;
		}
	}
	return $query_args;
}, 10, 2 );

// Modify the um_get_members query (custom usermeta table).
add_action( 'um_pre_users_query', function( $directory, $directory_data ) {
	global $wpdb;
	global $um_custom_filters;
	foreach( $um_custom_filters as $f ) {
		if ( ! empty( $_POST[ $f['key'] ] ) && ! empty( $f['fields'] ) ) {
			$value = sanitize_text_field( $_POST[ $f['key'] ] );
			$table = $wpdb->prefix . 'um_metadata';
			$alias = 'umm' . $f['key'];
			$keys  = "'" . implode( "','", $f['fields'] ) . "'";
			$like  = '%' . $wpdb->esc_like( $value ) . '%';

			$filter_query = $wpdb->prepare(
				"INNER JOIN %i AS %i ON ( %i.user_id = u.ID AND %i.um_key IN ({$keys}) AND %i.um_value LIKE %s )",
				$table,
				$alias,
				$alias,
				$alias,
				$alias,
				$like
			);

			$directory->joins[] = $filter_query;
		}
	}
}, 10, 2 );

This code adds three filters:

• Filter Make displays members who have needed value in fields with meta key make1, make2 or make3.
• Filter Model displays members who have needed value in fields with meta key model1, model2 or model3.
• Filter Year displays members who have needed value in fields with meta key year1, year2 or year3.

Extend the $um_custom_filters array to add more filters.
Extend the fields array in the filter array to add more related fields.

Screenshots

Fields which data are used for filtering members.

Added custom filters in the member directory.