how to get the icloud annual plan?

Sorry, but iCloud storage plans are on a monthly basis only:

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You can upgrade your iCloud storage plan from your iPhone, iPad, iPod touch, Mac, or PC. Choose from a total of 50GB, 200GB, or 2TB. You can even share the 200GB and 2TB plans with your family. After you upgrade, we'll bill you monthly.1 See the monthly pricing and plans per country or region below.

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copied from: iCloud storage plans and pricing - Apple Support

You can prepay for a year of iCloud storage using Apple gift cards, but you will not get a discount for buying a year in advance. See: https://www.apple.com/shop/gift-cards