It will not be advisable to make transactions in bitcoin within a country where cryptocurrency transactions are illegal by the law. But Imagine this scenario that someone has been using their bitcoins for transaction secretly successfully, and then one day decides to use the bitcoin that they have to make payment for something like a property to the owner of the property, If there is this kind of problem for instance where the owner of the property decides to claim that they did not receive any money in bitcoin, and the case is taken to a law court, what do you think the outcome of the case will be?
If proofs of payment are provided but in cryptocurrency, do you think the court will consider it even though transactions are tagged illegal with it? or will the case be thrown out and the owner of the property with the false claim of not receiving the money be allowed to go freely?
I am from Indonesia in here Bitcoin and some other cryptocurrencies are allowed, but only for commodities, not for the payment method. Regarding your mentioned case where Bitcoin was used in one particular property's payment, I have never seen anything like that happened but as far as I understand that transaction itself would not be considered valid in the court. Even if the buyer can prove that the Bitcoin payment was made, since crypto is illegal to use in transactions, the court would most likely side with the property owner if they claim never to have received the payment.
It is also dangerous, because if it goes to the court, any evidence that a crypto might involve could be discharged, and the buyer will be facing penalties for breaking Indonesian regulations. In countries like Indonesia, where cryptocurrency trading is regulated but not allowed for options of payment, it is safer to stay in line with the legality of modes of transaction on large purchases, such as through a bank transfer or in cash in advance when buying property.