I have my software update to 13 but don’t have dark mode

Ok. So based on the photo, you don’t have iOS 13 yet, you still need to download and install it. And secondly, iOS 13 does not run on an iPhone 6, so you have an iPhone 6s.

You can't have iOS 13 on your 6 Plus. The highest iOS you can have on a 6 Plus is 12.4.2.

Connerfromgrinnell is correct.

In addition, the phone is in low power mode and is below 50% so it won't update until it is charged to at least 80%.