Type {} is missing the following properties from type {}: length, pop, push, concat, and 29 more

Question

const function= () => {
    facets = useSearchMoreFacets(
        variables
    );
};

type UseSearchMoreFacets = {
    facets: MappedFacet[] | undefined;
};

export const useSearchMoreFacets = (variables): UseSearchMoreFacets => {
    const { data } = useQuery<Data, QuerySearchArgs>(QUERY, {
    variables: {
       //variables
    }
});
    return {
       facets: facetMapper(data?.search?.facets, user)
    };
};

const facetMapper = (facets: Facet[] | undefined, user?: User): 
MappedFacet[] | undefined => //stuff//

type ValueType = {
    value: string;
    count: number;
};

export type MappedFacet = {
    id: string;
    values: ValueType[];
};

i have a variable facets, which has already been declared and i need to change it in a specific event called via function

now if i try to overwrite facets using useSearchMoreFacets using the same query as in the working initial declaration, i get the error :

Type 'UseSearchMoreFacets' is missing the following properties from type 'MappedFacet[]': length, pop, push, concat, and 29 more

the difference to the inital declaration is, that i use more return values to assing them directly to more variables. but since i specififed only this sole return vale i dont see the problem in that