Save ACF repeater fields in serialized format to save meta rows

functions.php

<?php
/**
 * This is example code, not directly use on the Production site.
 */

add_action( 'acf/save_post', function ( $post_id ) {
	// Skip options page and revisions/autosaves.
	if ( $post_id === 'options' || wp_is_post_autosave( $post_id ) || wp_is_post_revision( $post_id ) ) {
		return;
	}

	// Field key for pi_repeater_slides.
	$field_key  = 'field_68416c37f6cf4';
	$field_name = 'pi_repeater_slides';

	if ( ! isset( $_POST['acf'][ $field_key ] ) ) {
		return;
	}

	$slides_data = $_POST['acf'][ $field_key ];

	// Save serialized array in a single meta key.
	update_post_meta( $post_id, "serialized_{$field_name}", maybe_serialize( $slides_data ) );

	global $wpdb;

	// Delete all post meta keys related to ACF's default repeater format.
	$meta_key_like = $wpdb->esc_like( $field_name ) . '%';

	$wpdb->query(
		$wpdb->prepare(
			"DELETE FROM {$wpdb->postmeta} WHERE post_id = %d AND ( meta_key LIKE %s OR meta_key LIKE %s )",
			$post_id,
			$meta_key_like,
			'_' . $meta_key_like
		)
	);
}, 20 );

add_filter( 'acf/load_value/name=pi_repeater_slides', function ( $value, $post_id, $field ) {
	$serialized = get_post_meta( $post_id, 'serialized_pi_repeater_slides', true );

	return $serialized ? maybe_unserialize( $serialized ) : [];
}, 10, 3 );