The US at least, millions of Americans are paid every day for their work in untraceable physical cash, and there are no laws against it all of these years later.
Cash is traceable because the dollar notes have serial numbers on them. That's how they track down gun and drug sales for instance.
Foreign currency though.... can't be traced by the local government.
Most people who try to hide their fiat money without using crypto do so with offshore banks, as these cannot be investigated for the funds as they are in some secret jurisdiction like Panama or something.