Is the complaint of the wronged against the wrongdoer before others considered backbiting, and is it considered a substitute for taking one's rights, and is the wronged person sinful if he warns people against the wrongdoer who does not accept advice?

The wronged person speaking about the injustice of the oppressor is not sinful and is not considered backbiting (gheebah), especially if the oppressor does not accept advice. The proof for this is Allah's saying: (Allah does not like the public utterance of evil, except by one who has been wronged) [An-Nisa 4:148], and the Prophet (peace be upon him) said: "The delay of a wealthy person (in paying debts) makes his honor lawful (for defamation) and his punishment (for imprisonment)." The words of the wronged person do not nullify their right or remove the sin from the oppressor, except through forgiveness. Even if supplicating against them reduces the sin, as stated in the Hadith: "Do not reduce his sin thereby." The supplication of the wronged person is answered, for the Prophet (peace be upon him) said: "There are three whose supplications are not rejected: a just ruler, a fasting person until he breaks his fast, and the supplication of the wronged. Allah raises it above the clouds on the Day of Resurrection, and the gates of heaven are opened for it, and the Lord, the Mighty and Majestic, says: 'By My glory, I will surely help you, even if after a while.'"