I am not an El Salvadorian, so this is based on what I have been reading on news.
So if I really get you, you mean that it is a must that a merchant will accept bitcoin as a payment from the buyer, and then after accepting the payment from the buy they can decide whether they want it to be converted immediately to fiat, by who?
The official El Salvadorian wallet is called Chivo bitcoin wallet, the wallet can automatically convert bitcoin to dollar, the wallet can handle the payment you are asking about automatically.
If merchants accepts bitcoin, and since compulsory for them, is it the bank that converts it to fiat for them based on their preference?
All I know is that the Chivo wallet handles that automatically. Dollar can be withdrawn from the Bitcoin ATM, I mean the bitcoin holdings can be withdrawn into cash from the bitcoin ATM. I do not think there should be bank involvement about this, even 70% of Salvadorians are not making use of bank.
Chivo wallet is a custodial wallet, all the conversion are just representation of numbers, nothing happens on the blockchain while converting from dollar to bitcoin or from bitcoin to dollar which will also makes the fee to be zero, I mean while paying in bitcoin but accepting dollar or paying in dollar but accepting bitcoin. I do not read about this, but would be how it will be operating. So bank is not necessarily involved.
I don’t think this is something that should be forced, it’s a thing of choice, people should decide for themselves.
If you think about how this operate, you will notice is not by force, only that merchants will have Chivo wallet or any wallet of their choice, but they can still decide to finally receive the pay in bitcoin or dollar.