how can I confirm my laptop hard drive is backed up to icloud?

You posted in the "iCloud on my PC" forum so this answer is about Windows PCs.

Apple has iCloud Backup for iPhones and iPads but not for computers. With a Windows PC you can install iCloud for Windows and choose to sync some data to iCloud. See: Set up and use iCloud for Windows - Apple Support

If yo want to verify the data has synced, you can use the computer's internet browser and log into icloud.com and view the data there.