The EU is paying for the new shelter, not Russia or Ukraine. The construction of the old shelter/sarcophagus is a lie. They're still running about 10 of these RMBKs in Russia proper.
The new shelter is not even on the same scale of intent as the old sarcophagus. Never mind the shortcomings of the sarcophagus, its intent was to be a shield for radiation. It is falling in due to its own weight, and hasty construction. But as of now it is serving its purpose, although badly in need of repair.
The new shield is nothing more than dust cover. Made of thins sheet steel, it is designed to keep the dust of future work on the sarcophagus contained. It is not itself designed to block radiation. Its mostly dual concentric layers of 1 mm thick correlated sheet steel and aluminum held up by a system of trusses. It is not designed to be radiation proof.
Once in place, the new structure should contain radioactive dust, preventing any atmospheric contamination should the old sarcophagus collapse. The new building is expected to last anywhere from 100 to 300 years.