How can I access data from an iPhone 8 Plus with a CPU shortage that doesn't power on?

If your phone has a short circuit, and won't turn on, there is no way to retrieve data using the phone. Any data which exists only on that phone is as good as gone.

Hopefully you were synchronizing data to iCloud (e.g., using iCloud Photos) and making backups. While there is no way to see what is in a backup without restoring it (wiping the target phone in the process), you can see things that you were synchronizing to iCloud by logging into https://www.icloud.com/ from just about any modern Web browser (on a Mac, Windows PC, Linux PC, or even a C

You don’t.

You can access the backups you made of your phone.