[SubuSS]

What you want to do is encrypt/anonymize per user information using a translation layer that also gets backed up. In case of a gdpr request, you delete this mapping / key and voila: data cleanup. The backup data becomes unusable.

But this obviously means building an extensive system to ensure the encoded identifier is the only thing used across your system (or a giant key management system).

In the past I’ve been a part of systems at exabyte scale that had to implement this. Hard but not impossible. I can see how orgs try to ‘legalese’ their way out of doing this though because the only forcing function is judicial.