This is the current type declaration for Select:

export interface SelectProps extends BasicSelectProps {
clear?: boolean | { position?: 'top' | 'bottom'; label?: string };
closeOnChange?: boolean;
defaultValue?: string | number | object | (string | number | object)[];
multiple?: boolean;
selected?: number | number[];
value?: string | JSX.Element | object | (string | number | object)[];
}

but the docs say that value can be a number too, so I would recommend updating components/Select/index.d.ts to say this.

export interface SelectProps extends BasicSelectProps {
clear?: boolean | { position?: 'top' | 'bottom'; label?: string };
closeOnChange?: boolean;
defaultValue?: string | number | object | (string | number | object)[];
multiple?: boolean;
selected?: number | number[];
value?: string | number | JSX.Element | object | (string | number | object)[];
}

I'd file a pull request, but I don't know how.