PARIS—There was no instruction manual when IKEA’s Paris team set to work building a new kind of city-center store.

The Swedish furniture company’s ambition was to create a smaller version of its giant blue-and-yellow suburban stores for downtown consumers, to be replicated around the world. A quarter of the size of IKEA’s traditional outlets, the central Paris store—the first of this new type when it opened in 2019—would need to be radically different, they decided.