Is it forbidden for the first wife to file for divorce from her husband who married another, when he is capable of fairness and equality, and does the divorce take place if it occurs through this lawsuit?

If you are capable of fulfilling the requirements of marrying a second wife and maintaining justice between wives, then polygyny is permissible for you. It is not permissible for the first wife to demand a divorce because of this marriage, otherwise, she exposes herself to the warning mentioned in the Hadith: "Any woman who asks her husband for divorce without any strong reason, the scent of Paradise will be forbidden to her." If a divorce occurs without your pronouncement of it, it is invalid, because divorce is in the hand of the husband, unless there is clear harm proven to the first wife and the Shariah judge rules for divorce due to this harm.