Is the money obtained by the wife through the courts considered a lawful or unlawful gain in this case?

If the marriage is fictitious and does not fulfill its pillars (arkan) and conditions (shurut), then the woman is not considered a wife, is not entitled to anything, and no divorce is needed. However, if the marriage fulfills its pillars and conditions, it is valid and its legal effects apply, and it does not matter if its intention was to obtain citizenship. It is not permissible to resort to man-made laws except out of necessity. The divorce decreed by man-made courts is not effective; rather, a divorce issued by a recognized Sharia authority is effective. The rights of a divorced woman vary depending on the circumstances of the divorce (before or after consummation). It is not permissible for the woman to take what the man-made court has decreed, such as half of the savings or a monthly salary. However, if you have consummated the marriage with her or had a valid private seclusion (khalwa sahiha) with her, then she is entitled to maintenance (nafaqa) from the time of consummation or seclusion. Marriage is a covenant and a solemn pact with noble objectives, and it is not permissible to treat it frivolously. Similarly, it is not permissible for a Muslim to seek to obtain citizenship of a disbelieving country except out of necessity.