How sound is the reasoning that silence regarding the condemnation of certain reprehensible acts, such as music and mixing in celebrations, is better than having the perpetrators commit a graver sin? Is it permissible for me to remain silent about condemning these acts in this situation? And is my decision not to attend birthday celebrations, even if it leads to cutting ties, correct?

The questioner cannot remain silent about the evil he sees from his friends. Rather, it is obligatory for him to denounce them every time he sees them committing an evil, because the Prophet, peace and blessings be upon him, said: "Whoever among you sees an evil, let him change it with his hand; if he is unable, then with his tongue; if he is unable, then with his heart—and that is the weakest of faith." His knowledge of his own sins and transgressions should not prevent him from denouncing them, as it is not a condition for the denouncer to be free of them. The argument to abandon denunciation so that they do not fall into a greater evil is not valid in this case. In fact, their continued mixing may lead them to greater evils like fornication and drinking alcohol. Denunciation may be abandoned in some cases if it is highly probable that it will lead to a greater evil, as Ibn Taymiyyah mentioned regarding the Tatars. The questioner is advised to fear Allah, stay away from sins and those who commit them, and avoid their gatherings.