Is it permissible to distribute Zakat al-Mal (money) in the form of monthly salaries to several individuals, such that a portion of the Zakat is paid each month, and then the remaining amount is calculated and paid at the end of the year?

If the distribution of money is in the form of monthly salaries during the year, then there is nothing [wrong] with it, because it is considered an advance payment of Zakat, which is permissible. Ibn Qudamah detailed the categories of advancing Zakat in "Al-Mughni":

1. No change in the recipient's status: The amount paid is sufficient on behalf of the zakat payer. 2. Change in the recipient's status: It is also sufficient, and this is what Abu Hanifa said, contrary to Al-Shafi'i. 3. Change in the wealth owner's status: Abu Bakr and Al-Qadi said that the money should not be reclaimed from the poor person, while Al-Shafi'i and Ibn Hamid said: If the zakat payer informed the poor person that it was an advance payment of Zakat, then he can reclaim it if his status changes, otherwise not.

However, if you distribute Zakat after the end of the year, this is not permissible except for a valid considered interest, because Zakat is a right of the poor that must be paid when it becomes due.