Can I update my iPhone 7 to iOS 16.3

Hello ~ No …unfortunately not. If you need iOS 16 you will need a newer iPhone. If you choose to purchase a second hand iPhone please take a moment to read these links by clicking on below so you can make an informed decision…

Activation Lock for iPhone, iPad, and iPod touch - Apple Support

Also:

The All Too Common SAD Reality of Buying a Used iPad/iPhone

~Katana-San~

Your iPhone 7 can only update as far as iOS 15.7.3

An iPhone 7 cannot update past iOS 15.