These types are defined in DefinitelyTyped, but are not located here. Because of this, the following is valid:
const items = _(someObj)
.pickBy((item) => ...)
.mapValues((item) => ...)
.value();
but this is invalid:
const items = _.chain(someObj)
.pickBy((item) => ...)
.mapValues((item) => ...)
.value();