“Whoever among you sees an evil action, let him change it with his hand (by taking action); if he cannot, then with his tongue (by speaking out); and if he cannot, then with his heart (by hating it and feeling it is wrong), and that is the weakest of faith.” [Muslim].
Depends on your capability of effecting positive change and how much good you will be able to do without making the situation worse in Allah's sight than it is.
Backbiting is gossiping that is not aimed towards working to fix a deteriorating situation and returning to the will of Allah :swt: - but rather putting evil into people's hearts and thereby making the situation worse by spreading the normality of haraam actions.
And Allah :swt: knows best.
Abu Huraira reported: The Messenger of Allah, peace and blessings be upon him, said, “The strong believer is more beloved to Allah than the weak believer, but there is goodness in both of them. Be eager for what benefits you, seek help from Allah, and do not be frustrated. If something befalls you, then do not say: If only I had done something else. Rather say: Allah has decreed what he wills. Verily, the phrase ‘if only’ opens the way for the work of Satan.”
Source: Ṣaḥīḥ Muslim 2664
Grade: Sahih (authentic) according to Muslim
An-Nawawi said, “‘It opens the way for the work of Satan’ means he casts into the heart opposition to the divine decree and Satan tempts him with it.”
Source: Sharḥ Ṣaḥīḥ Muslim 2664
عَنْ أَبِي هُرَيْرَةَ قَالَ قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ الْمُؤْمِنُ الْقَوِيُّ خَيْرٌ وَأَحَبُّ إِلَى اللَّهِ مِنْ الْمُؤْمِنِ الضَّعِيفِ وَفِي كُلٍّ خَيْرٌ احْرِصْ عَلَى مَا يَنْفَعُكَ وَاسْتَعِنْ بِاللَّهِ وَلَا تَعْجَزْ وَإِنْ أَصَابَكَ شَيْءٌ فَلَا تَقُلْ لَوْ أَنِّي فَعَلْتُ كَانَ كَذَا وَكَذَا وَلَكِنْ قُلْ قَدَرُ اللَّهِ وَمَا شَاءَ فَعَلَ فَإِنَّ لَوْ تَفْتَحُ عَمَلَ الشَّيْطَانِ
2664 صحيح مسلم كتاب القدر باب في الأمر بالقوة وترك العجز والاستعانة بالله وتفويض المقادير لله
قال النووي فَإِنَّ لَوْ تَفْتَحُ عَمَلَ الشَّيْطَانِ أَيْ يُلْقِي فِي الْقَلْبِ مُعَارَضَةَ الْقَدَرِ وَيُوَسْوِسُ بِهِ الشَّيْطَانُ
2664 شرح النووي على مسلم
I would add that "if" in this context should only be used for learning lessons and doing better next time.