How to update a refurbished iPhone 7 beyond iOS 16.5?

The iPhone 7 cannot update to any iOS 16 version, so no sense in spending time looking for that or "trying everything".

To run iOS 16, you would need to have an iPhone 8, iPhone 8 Plus or iPhone X.

Did you have another question?

If this is an iPhone 7, I do not see how it could be running iOS 16.5 now. The iPhone 7 can only update as far as the latest release of iOS 15, currently iOS 15.8.3.

About iOS 15 Updates - Apple Support

Hello~ If you have an iPhone 7 as indicated…you can’t update to iOS 16 at all. The highest version of iOS 15 is the limit.

~Katana-San~