Is he permitted to do that, since my husband made my divorce conditional upon my waiving of the deferred mahr?

If a husband conditions divorcing his wife on her relinquishing the deferred dower (mu'akhkhar):

If the husband is harming her, it is not permissible for him to take anything from her. Rather, he should divorce her and give her her full rights.

However, if he is not harming her, but she dislikes staying with him, then he may compel her to seek khul' (divorce at the wife's instance, often with a compensation) and ask her for money or for her to relinquish her dower.

It is not permissible for a woman to seek divorce or khul' unless there is a legitimate شرعي excuse.