Android
Change the Google Backup Account auf Android
Android backs up app data, call history, and device settings to a Google account in the background. When several accounts are signed in on the same phone, the system keeps using whichever account was set as the backup target, even if that is not the one you actively use for Drive, Photos, or Gmail.
The backup target lives in the storage settings, not in the individual Google account menu. To change it, go to Settings ➔ System ➔ Backup ➔ Account storage ➔ Choose a Backup account and pick the account you want to use going forward.
Switching the account does not move existing backups between accounts. Older backups stay tied to the account that created them, so a device restore only offers data from the account that was active at backup time.
If backups seem to be missing entirely rather than stored under the wrong account, check that backup itself is turned on before changing the target account. An account switch will not fix a backup that never ran.