uninstall.php

<?php
declare(strict_types=1);

if ( ! defined( 'WP_UNINSTALL_PLUGIN' ) ) {
	exit;
}

$icxcnika_delayed_cleanup = static function (): void {
	global $wpdb;

	delete_option( 'icxcnika_delayed_settings' );
	delete_option( 'icxcnika_delayed_seen' );
	delete_option( 'icxcnika_delayed_registry_key' );
	delete_transient( 'icxcnika_delayed_release' );
	wp_clear_scheduled_hook( 'icxcnika_delayed_registry_ping' );
	wp_clear_scheduled_hook( 'icxcnika_delayed_digest' );

	$names = $wpdb->get_col(
		$wpdb->prepare(
			"SELECT option_name FROM {$wpdb->options} WHERE option_name LIKE %s",
			$wpdb->esc_like( '_transient_icxcnika_delayed_rel_' ) . '%'
		)
	);
	foreach ( (array) $names as $name ) {
		delete_transient( substr( (string) $name, strlen( '_transient_' ) ) );
	}
};

if ( is_multisite() ) {
	$icxcnika_delayed_sites = get_sites(
		array(
			'fields' => 'ids',
			'number' => 0,
		)
	);
	foreach ( $icxcnika_delayed_sites as $icxcnika_delayed_site_id ) {
		switch_to_blog( (int) $icxcnika_delayed_site_id );
		$icxcnika_delayed_cleanup();
		restore_current_blog();
	}
} else {
	$icxcnika_delayed_cleanup();
}