How to shut down Windows 10 PC after Reset

I've just reset a Windows 10 PC, in order to pass it on to someone else. It's a Microsoft Surface Pro 4.

It's now prompting me to set it up, starting with selecting the language.

I want to shut it down, to send it on to its next owner, who will do the set-up.

No amount of holding down the power button is actually tuing it off.

Are there any tricks, please?

(I'm worried that if I let the battery go flat, and it won't it might be considered a security risk if investigated in the post)