iCloud backups will be deleted on iPhones with iOS 8 or earlier

In a new support document, Apple has revealed that starting December 18, 2024, devices running iOS 8 or earlier will no longer be eligible for iCloud backups, and any backups stored in iCloud will be deleted.

How to keep your devices and data backed up in iOS 8 or earlier - Apple Support

https://support.apple.com/en-us/120863

iCloud backups will be deleted and discontinued for iPhones running iOS 8 and older
https://9to5mac.com/2024/11/18/icloud-backups-will-be-deleted-and-discontinued-for-iphones-running-ios-8-and-older/

Apple allows you to back up information and settings stored on devices such as iPhones, iPads, and iPod Touches to iCloud. This means that even if you purchase a new device, you don't have to set it up from scratch, and you can start with the same environment as before by logging in and restoring it from a backup.

'Starting December 18, 2024, we will require iOS 9 or later to back up your device to bring it closer to our published minimum software requirements. You can use our service as usual until that date, but after that, your backup data will be deleted unless you update to iOS 9 or later,' Apple said in a support document published on November 18, 2024.

In addition, after December 18, 2024, devices running iOS 8 or earlier will no longer be able to create new backups or access existing backups. To continue using iCloud backups, you will need to update to iOS 9 or later.

This doesn't mean your device will become unusable -- all of your apps, data, and content will remain on it, and you can still manually back up your device to a PC or Mac using iTunes or Finder.