No manual intervention needed just track everything and retain the data for a long time. Then you can query the database for all serial numbers your target has ever taken out of an ATM and where they where returned. Circulation will diffuse these results somewhat but that follows a normal distribution. That means it is much more likely that a bill that was spent at a store by your target which is given out again as change, is more likely to be spent at another store near that original store. Aggregate this information over a couple of weeks or months and you will get a heatmap of locations to check out. You can run this operation automatically on all bank accounts if you want. Threshold the heatmap at some significant value and you get a list of stores visited by each person with X% probability.

I ONLY give other people cash, all my other purchases are debit/credit.

If you always use card payments whenever it's possible, it obviously isn't necessary to analyze your cash transactions to learn where you are because you are already disclosing it :)

Like MOST people and stores since Covid

There are close to 2 billion unbanked people in the world. In the US, it's less than 6% nationally, but over 10% in some states.

Many people who are not unbanked also often avoid electronic payments for privacy/security and other reasons.

The cash serial number tracking being described in this thread is useful for locating the neighborhoods frequented by someone who (a) avoids using electronic payments, and (b) maybe obtains cash from an ATM (or perhaps check-cashing service, in the case of an unbanked person) in places other than the neighborhoods they live in or frequent.