Is it permissible, from a Sharia perspective, to work in a software company that serves both usurious (interest-based) and Islamic banks, with a focus on systems shared between them, especially considering a previous fatwa from "Islam Q&A" prohibiting assistance in usury, and a fatwa from the Egyptian Dar al-Ifta permitting it, and the employee's desire to limit work to Islamic banks only?

"A person is commanded to seek out the permissible (halal) and to abstain from forbidden (haram) things and doubtful matters (shubuhat). Working in usurious institutions is forbidden, even if one is not directly involved in usury itself, because it constitutes cooperation in sin. Therefore, if your work in that company is with Islamic banks, there is no objection to it. However, if it is with usurious banks, it is not permissible, because that which leads to the forbidden is itself forbidden. You should only work in the permissible areas for that company, such as Islamic banks and the like. If you cannot limit yourself to working only in the permissible, then seek other employment, for whoever gives up something for the sake of Allah, Allah will compensate him with something better."