Isn't it much more likely that a court would order the code published instead of restricting the use of an extremely popular payment system and brake half of the economy?

I mean, they blocked WhatsApp (95+% usage) before so who knows, but it seems unlikely it will actually affect the average person.

I mentioned 'Mandado de Segurança' not to suggest halting Pix, but because, yes, it's the relevant instrument in Brazilian law for forcing public agencies to comply with legal duties — in this case, transparency around public code. Courts would not block Pix itself unless something extreme happened. They might simply compel BCB to release the code if the legal conditions are met.