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?
After taking the case to the law court, the government will have to decide what to do since they are the ones that have the law of that country. To me, you think the buyer will face more problems than the seller because he will definitely pay for the property if he is still interested in buying the property, and after that, you will get punished by the government for disobeying the law of that country. And he will pay for the property in fiat. Although the seller may also get punished for accepting currency that is illegal by the government, I definitely know they must be punished.