The neatest way I heard is to store PII in an encrypted form and then delete encryption keys when a user requests deletion. That requires the keys to be in a different backup pipeline though.

You still have their data and anyone who bypasses the restoration script can get it so no.

This is not true. The prevailing opinion is that backups do not need to be modified and that it’s enough to delete at restore time (and to of course not process the data again).