> So if you sell a house and want to buy a new one, you have to pay for a mortgage you don't need?

You misunderstand.

We are talking hard paper cash here. It might help if we quote a translated excerpt here :

This practice is now being abolished by the introduction of Sec. 16a GwG. From 1 April 2023, it will only be possible to purchase real estate using means of payment other than cash, crypto assets, gold, platinum or precious stones. All parties to the transaction are required to present satisfactory proof of payment, for example a payment confirmation from a financial institution.

(source of excerpt https://www.gvw.com/en/news/blog/detail/prohibition-on-cash-...)

Cash as in the physical object. Bank transfers are different.

I believe in this case, cash refers to physical bills, not how it's normally used in conversation (at least in the UK) to mean buying without a mortgage (via bank transfer).

Does Germany have no equivalent to a money order?

Cash in this context means literal cash.

Electronic transfers such as ACH would be allowed.

No u have to do a bank transfer -in cash here means literally in cash...

No, you would have money in a bank account, and transfer the money to the receipients bank account. No cash payment needed.

Absolutely not, it simply means the payment must be done via the banking system. Electronic = mostly traceable.