Except for simply not collecting the data, the only other option is making the cost of retrieval be equivalent or greater, irreducibly, to the expected value of keeping it.
Approximately, the digital equivalent of having a human rifle through filing cabinets to get to that one folder that is actually important.
To this day, the only reliable way to achieve this has been printing things on paper, especially if put in individual folders do that even OCR efforts take some human work.
Time spent by human hands are, in a way, the only somewhat fair currency to measure privacy in.
Approximately, the digital equivalent of having a human rifle through filing cabinets to get to that one folder that is actually important.
To this day, the only reliable way to achieve this has been printing things on paper, especially if put in individual folders do that even OCR efforts take some human work.
Time spent by human hands are, in a way, the only somewhat fair currency to measure privacy in.