Earlier quoted context omitted.
There is no such central database, for one. All the transactions are controlled by multiple independent parties, whose interests do not align to do that as they’d lose their customers to their competitors when it came out what was happening. Some of the data does go through central clearing at some step (ACH, Fedwire), but credit card charges, Zelle, cash, checks deposited at the same bank, etc. do not.
Since we are talking about nazis, it doesn’t really matter what is in the interest of independent banks and CC companies. The nazis will simply send the storm troopers to them and get the lists of people donating to synagogues, easy peasy. With cash, you stay out of those databases in the first place.
Definitely not impossible, but much harder than if there was a single centralized system - dramatically harder.
Cash is king though, as you say.