How to purchase a one year Apple TV subscription

First subscribe to Apple TV+ (monthly), then change the billing period to annual (if offered for that subscription). It is two steps.

How to switch to a different subscription plan - Apple Support

In contrast, Apple One doesn’t have an annual option.

On your iPhone go to Settings, tap your Apple ID (name and profile pic at top of list), then look for Subscriptions in first section. Tap Apple TV+, then tap “See All Plans.” From there you can choose yearly. Good luck!