What is the ruling on working for joint-stock companies or anonymous companies for a computer engineer, knowing that the tasks he will perform are permissible (halal)?

The ruling on working in companies depends on the nature of their work: If the core of their activity is in the forbidden (like selling alcohol), then it is not permissible to work for them, even if the work itself is permissible; because it constitutes assistance in the forbidden. However, if the core of their activity is permissible, or if the permissible predominates, even with the existence of some forbidden transactions, then it is permissible to work for them in matters not related to the forbidden transactions.