Unclear or non-working where function for query with date field

[pandabrand]

I'm trying to build a filter mechanism. I have this function:

    const filter = (filters: IFilter[]) => {
        const queries: any[] = []

        filters.forEach((field) => {
            queries.push(
                stack
                .contentType(contentType)
                .entry()
                .query()
                .where(field.uid, QueryOperation.INCLUDES, field.params)
            )
        })

        query.queryOperator(QueryOperator.OR, ...queries)

        query
        .includeCount()
        .paginate({skip: 0, limit: perPage})
        .orderByDescending(sortField)
        .find()
        .then((res) => {
            dispatch({
                type: 'ADD_ENTRIES',
                payload: {
                    entries: res.entries ?? [],
                    count: res.count ?? 0
                }
            })
        })
    }

I can't find any documentation whether the date field is stored as a string or a number. In the example I'm testing the field.params is carrying an array of years as a string. I have also tried converting to an int. I always get an empty result. Since I can't find any documentation to verify whether or not this is correct, I'm also reaching out in case this is an issue.