Can I update my iPhone 8 Plus?

Your tag line says that you have an iPhone 8 Plus running iOS 14. So it looks like you can upgrade to iOS 16.

An iPhone 8 Plus cannot run iOS 17. (See: iPhone models compatible with iOS 17 - Apple Support)

An iPhone 8 Plus can run iOS 16. (See: iPhone models compatible with iOS 16 - Apple Support)

Update your iPhone or iPad - Apple Support

Yes to iOS 16.7.1, if you have a good Wi-Fi connection....and....enough free space on your phone.

No, if you are asking if the phone can update to iOS 17.

What happens if you tap Settings > General > Software Update?