What we did (and legal was OK with it) was to create a "GDPR Delete" function in the admin backend. It doesn't actually delete, but sets a soft delete identical to the regular user delete function and overwrites any PII with stuff like name:gdpr_delete_name_xxxx

That way log and system context is available for debugging, but the system no longer holds any PII. It does delete some logs, but anonymizing data seemed better than hard deletion. It wasn't hard to do, it took legal longer to approve than writing and testing the code and has come in handy a few times for debugging errors.

Edit: typo