◇ Could this help me?
Yes. Cryptographic erasure, also called crypto-shredding, is a recognized and sound answer to data that lives in immutable backups, and the video describes the mechanism correctly. Adopt it with one addition the video skips: the guarantee is only as strong as the key management, so the keys need their own isolated store, their own backup and rotation policy, and a destruction path that can be audited. This is a general practice.
Assess whether per-user cryptographic erasure is feasible for this codebase. Identify which tables hold user personal data, propose a per-user key scheme with a separate key store, describe exactly what deletion would destroy and what would remain readable or unreadable in backups, and list the operational costs and risks including key backup, rotation, loss, and audit. Produce the assessment only. Do not implement anything yet.