Is it obligatory to leave mixed-gender work in which wrongdoings occur, especially when there is no financial incentive to continue in it? And can an unfruitful Istikhara be considered an indication that it must be left?

It is not permissible to work in a mixed environment except out of necessity or dire need. In such a case, it is stipulated that one adheres to the Sharia guidelines, such as being cautious not to be lenient in interacting with men. If the work is forbidden, then istikhara (seeking guidance from Allah) is not permissible for it, because istikhara is for permissible matters. It is also known that a woman's decision to stay in her home is better for her.