What is the ruling on the penalty imposed on those who are late in paying housing rent, is it usury (riba), is working in this office helping in usury, and what is the ruling on the salary earned from it?

The amount of rent that the tenant delays in paying is a debt. A late payment penalty for a debt is not permissible to impose, because it is usury (riba). The Islamic Fiqh Council of the Muslim World League has issued a fatwa prohibiting late payment penalties.

Some jurists are of the opinion that penalties imposed by the state are discretionary punishments (ta'zeer) and not compensation for the injured party.

The correct view is that imposing a late payment penalty is forbidden.

As for working in the office and receiving its salary, there is no harm in it, because collecting the penalty is not the primary purpose of the work. However, one must refrain from collecting these penalties in the future.