Is Zakat due on money that has been invested through Mudarabah (profit-sharing), from the date of the completion of the work and the calculation of profits, or from the date of its receipt? And does the principal (capital) enter into the value of Zakat?

The zakat on profit is subject to the zakat on capital. Zakat becomes due on both capital and profit at the end of a full year (hawl) from the acquisition of the asset, whether the profit has been received or not, as long as its payment is guaranteed. If its payment is not guaranteed, then zakat is not obligatory on it until it is received, at which point zakat is paid for the past period. If the money is invested in purchasing real estate for sale, its hawl is not interrupted, and its zakat becomes due by appraising the property at the time of the original capital's hawl. The zakat hawl must be calculated according to the Hijri months.