No, you cannot currently buy iCloud storage on a standard annual plan. While Apple offered yearly options in the past, they transitioned to a strictly monthly subscription model in 2015.
: You can manually add funds to your Apple ID balance or redeem Apple Gift Cards to cover the cost of 12 months at once. can i buy icloud storage annually
: This balance is shared across all Apple services. If you purchase apps, movies, or other subscriptions, those funds may be depleted sooner than expected. No, you cannot currently buy iCloud storage on
However, you can effectively "prepay" for a year by using the following workarounds: : This balance is shared across all Apple services
: If you have an exceptionally old annual plan that has never been interrupted or changed, it may still renew annually, but these cannot be modified or re-purchased if cancelled. Current iCloud+ Monthly Tiers iCloud+ plans and pricing - Apple Support