After repentance, is it obligatory to seek forgiveness from everyone one has backbitten, and what should one do if one cannot reach them or fears angering them?

Allah has forbidden backbiting and depicted its perpetrator in a repulsive image in His exalted statement: ﴿And do not backbite each other. Would one of you like to eat the flesh of his brother when dead? You would detest it. And fear Allah; indeed, Allah is Accepting of repentance and Merciful.﴾ One must hasten to repent to Allah, and repetition of backbiting does not prevent the acceptance of repentance; for sound repentance is accepted even if it is repeated. Repentance entails ceasing the sin, regretting it, and resolving not to return to it, and seeking forgiveness from the person whose right was violated if possible. Otherwise, repentance between you and Allah suffices if seeking forgiveness is difficult or would lead to greater harm.