I'm not sure if this a 100% correct summary of what happened in Germany last year, but:
While the German Federal Constitutional Court has long reserved the power to reject EU actions that manifestly exceed EU competences or violate Germany’s constitutional identity, it was commonly thought that the Court was barking without biting. The ground-breaking judgement delivered on 5 May changed this. Although the ECB’s bond-buying programme had been ruled legal by the European Court of Justice, Germany’s Federal Constitutional Court set this decision aside for significantly exceeding EU competences on monetary policy and interfering with national competences on economic policy. It held that the ECB exceeded its powers by not assessing the effectiveness and collateral damage caused by the bond-buying programme. The Karlsruhe Court ordered the Bundesbank to end its participation in the ECB stimulus programme unless the ECB adopts a new decision demonstrating the proportionality of the programme within three months. In the absence of such an ECB decision, the Bundesbank would have to disregard either a Federal Constitutional Court judgement or its obligations according to EU law.
The ECJ reacted to the judgement by maintaining that it was the only institution authorised to rule that an EU institution violates the EU’s founding treaties. The EU Commission President Ursula von der Leyen stressed that rulings of the ECJ are binding on national courts and that the Commission was looking into opening infringement proceedings against Germany.
And the EU actually did start that 13 months later.
Among the key decisions announced [...] was a “letter of formal notice to Germany for breach of fundamental principles of EU law, in particular the principles of autonomy, primacy, effectiveness and uniform application of Union law, as well as the respect of the jurisdiction of the European Court of Justice” by the German court in its decision in the PSPP case. Specifically, the Commission faulted the court for declaring the ECB “to be ‘ultra vires’, going beyond its competence” and declaring the ECJ’s 2018 ruling in the case “to be ‘ultra vires’ – without referring the matter back to the Court of Justice. As a consequence, the German Court deprived a judgment of the European Court of Justice of its legal effect in Germany, breaching the principle of the primacy of EU law. This is the reason now for starting this infringement procedure….The Commission considers that the judgment of the German Constitutional Court constitutes a serious precedent, both for the future practice of the German Constitutional Court itself, and for the supreme and constitutional courts and tribunals of other Member States” The Commission gave Germany two months to reply to its concerns.
I read however commentary such that in the Economist:
The German court was playing with matches; its Polish counterpart doused the EU’s legal system in petrol and deliberately started a fire.
How does the Polish case differ in gravity from the German one?