This article [1] explains an important distinction between backups and archives.
"Backups exist in case information is accidentally destroyed. Backups should cover all information, but each one only needs to be kept for a short time: essentially however long it will take the organisation to discover the destruction. … Archives, by contrast, involve long-term storage of the organisation's history."
It concludes that it's probably not necessary to delete data from a backup — just keep a record of what requests for deletion were made, in the rare event that restoration from a backup is necessary.
And avoid storing personal data in archives, or else split it out by-person, so it can be deleted if required.
"Backups exist in case information is accidentally destroyed. Backups should cover all information, but each one only needs to be kept for a short time: essentially however long it will take the organisation to discover the destruction. … Archives, by contrast, involve long-term storage of the organisation's history."
It concludes that it's probably not necessary to delete data from a backup — just keep a record of what requests for deletion were made, in the rare event that restoration from a backup is necessary.
And avoid storing personal data in archives, or else split it out by-person, so it can be deleted if required.
[1] https://community.jisc.ac.uk/blogs/regulatory-developments/a...