It will at minimum be a fight. It won’t just sail through. Also whole governments being against means one of them might challenge the law in to European Court of Justice. Since as nation-states also often have, EU itself has charter of rights part in the fundamental EU treaties. It also has normal limit and share of powers. EU Council and Parliament aren’t all powerfull. ECJ can rule a directive or regulation to be against the core treaties like Charter of Fundamental Rights of the European Union.

Said charter does include in it right to privacy (which explicitly mentions right to privacy in ones communications) and protection of personal data. Obviously none of these are absolute, but it means such wide tampering as making encryption illegal might very well be deemed to wide a breach of right to private communications.

Oh and those who might worry they wouldn’t dare at ECJ… ECJ has twice struck down the data protection agreement negotiated by EU with USA over “USA privacy laws are simply incompatible, no good enough assurances can be given by USA as long as USA has as powerful spying power laws as it has”. Each time against great consternation and frankly humiliating black eye to the Commission at the time.

ECJ doesn’t mess around and doesn’t really care their ruling being mighty politically inconvenient and/or expensive to EU or it’s memberstates. They are also known for their stance that privacy is a corner stone civil right (as stated in the charter and human rights conventions also, their legal basis) and take it very seriously as key part of democracy and protection of democracy. Without free and private communications and expression there can be no free political discussion, without free political discussion there can be no democracy.