Index signature is missing in type (only on interfaces, not on type alias) #15300

interface IndexType {
     [key: string]: string;
}

interface doesNotWork {
    hola: string;
}
type doWorks = { hola: string };

let y: IndexType;

const correctA = { hola: "hello" };
const correctB: doWorks = { hola: "hello" };
//error should be assignable to y
const error: doesNotWork = { hola: "hello " };

y = correctA;
y = correctB;
y = error; //Index signature is missing in type 'doesNotWork'
y = {... error}; //workaround but not equivalent since the instance is not the same