This script support multi-attachment (gallery) field using dynamic field.

multi-attachment-jetengine

<?php
/**
 * Plugin Name: JetEngine - Get attachment file links (multi)
 * Description: Dynamic Field callback that supports single **and multiple** attachment IDs.
 * Version:     1.2.0
 */

if ( ! defined( 'WPINC' ) ) { die(); }

add_filter( 'jet-engine/listings/allowed-callbacks', 'je_multi_attach_link_callback', 10, 2 );
add_filter( 'jet-engine/listing/dynamic-field/callback-args', 'je_multi_attach_link_callback_args', 10, 3 );
add_filter( 'jet-engine/listings/allowed-callbacks-args', 'je_multi_attach_link_callback_controls' );

function je_multi_attach_link_callback( $callbacks ) {
	$callbacks['jet_engine_get_attachment_file_link'] = 'Get attachment file link(s) by ID';
	return $callbacks;
}

/**
 * Accepts:
 * - Single ID (int|string)
 * - Array of IDs
 * - Comma-separated IDs string: "12,34,56"
 * - JSON-encoded array string: "[12,34,56]"
 */
function jet_engine_get_attachment_file_link( $attachment_value, $display_name = 'file_name', $label = '', $is_external = '', $separator = '<br>' ) {

	// Normalize to array of IDs
	$ids = [];
	if ( is_array( $attachment_value ) ) {
		$ids = $attachment_value;
	} elseif ( is_string( $attachment_value ) ) {
		$trim = trim( $attachment_value );

		// JSON array?
		if ( str_starts_with( $trim, '[' ) && str_ends_with( $trim, ']' ) ) {
			$maybe = json_decode( $trim, true );
			if ( is_array( $maybe ) ) {
				$ids = $maybe;
			}
		}

		// Comma-separated fallback
		if ( empty( $ids ) ) {
			$parts = array_filter( array_map( 'trim', explode( ',', $trim ) ) );
			if ( $parts ) { $ids = $parts; }
		}
	} elseif ( is_numeric( $attachment_value ) ) {
		$ids = [ $attachment_value ];
	}

	// If still empty but value looks like scalar, try as single
	if ( empty( $ids ) && ! empty( $attachment_value ) ) {
		$ids = [ $attachment_value ];
	}

	$target      = '';
	$is_external = filter_var( $is_external, FILTER_VALIDATE_BOOLEAN );
	if ( $is_external ) { $target = ' target="_blank" rel="noopener"' ; }

	$links = [];

	foreach ( $ids as $id ) {
		$id  = is_numeric( $id ) ? intval( $id ) : 0;
		if ( ! $id ) { continue; }

		$url = wp_get_attachment_url( $id );
		if ( ! $url ) { continue; }

		switch ( $display_name ) {
			case 'post_title':
				$name = get_the_title( $id );
				break;

			case 'current_post_title':
				$name = get_the_title( get_the_ID() );
				break;

			case 'parent_post_title':
				$parent_id = wp_get_post_parent_id( $id );
				if ( ! $parent_id ) { $parent_id = get_the_ID(); }
				$name = get_the_title( $parent_id );
				break;

			case 'custom':
				$name = $label;
				break;

			default:
				$name = basename( parse_url( $url, PHP_URL_PATH ) );
				break;
		}

		$links[] = sprintf( '<a href="%1$s"%3$s>%2$s</a>', esc_url( $url ), esc_html( $name ), $target );
	}

	// Nothing found
	if ( empty( $links ) ) { return ''; }

	// Join by separator (default <br>)
	return implode( $separator, $links );
}

function je_multi_attach_link_callback_args( $args, $callback, $settings = array() ) {
	if ( 'jet_engine_get_attachment_file_link' === $callback ) {
		$args[] = isset( $settings['jet_attachment_name'] ) ? $settings['jet_attachment_name'] : 'file_name';
		$args[] = isset( $settings['jet_attachment_label'] ) ? $settings['jet_attachment_label'] : '';
		$args[] = isset( $settings['jet_attachment_is_external'] ) ? $settings['jet_attachment_is_external'] : '';
		$args[] = isset( $settings['jet_attachment_separator'] ) ? $settings['jet_attachment_separator'] : '<br>';
	}
	return $args;
}

function je_multi_attach_link_callback_controls( $args = array() ) {

	$args['jet_attachment_name'] = array(
		'label'       => esc_html__( 'Display name', 'jet-engine' ),
		'type'        => 'select',
		'label_block' => true,
		'default'     => 'file_name',
		'options'     => array(
			'file_name'          => 'File name',
			'post_title'         => 'Attachment post title',
			'current_post_title' => 'Current post title',
			'parent_post_title'  => 'Parent post title',
			'custom'             => 'Custom',
		),
		'condition'   => array(
			'dynamic_field_filter' => 'yes',
			'filter_callback'      => array( 'jet_engine_get_attachment_file_link' ),
		),
	);

	$args['jet_attachment_label'] = array(
		'label'       => esc_html__( 'Custom label', 'jet-engine' ),
		'type'        => 'text',
		'label_block' => true,
		'default'     => '',
		'condition'   => array(
			'jet_attachment_name'  => 'custom',
			'dynamic_field_filter' => 'yes',
			'filter_callback'      => array( 'jet_engine_get_attachment_file_link' ),
		),
	);

	$args['jet_attachment_is_external'] = array(
		'label'       => esc_html__( 'Open in new window', 'jet-engine' ),
		'type'        => 'switcher',
		'default'     => '',
		'condition'   => array(
			'dynamic_field_filter' => 'yes',
			'filter_callback'      => array( 'jet_engine_get_attachment_file_link' ),
		),
	);

	$args['jet_attachment_separator'] = array(
		'label'       => esc_html__( 'Links separator', 'jet-engine' ),
		'type'        => 'text',
		'label_block' => true,
		'default'     => '<br>',
		'description' => esc_html__( 'String to place between links (e.g., ", ", " | ", or "<br>")', 'jet-engine' ),
		'condition'   => array(
			'dynamic_field_filter' => 'yes',
			'filter_callback'      => array( 'jet_engine_get_attachment_file_link' ),
		),
	);

	return $args;
}