Is zakat obligatory on the principal amount deposited in an Islamic bank, or only on the monthly profits generated from it, knowing that these profits are the primary source for covering living expenses and the principal amount has completed its hawl (one lunar year)?

Zakat (definition) is obligatory on the principal amount of invested capital if it reaches the nisab (definition), and it is to be paid every time a lunar year passes over it. Zakat is also obligatory on its remaining profits, and these profits are to be paid along with the principal amount, as they are an increment to it.