What is the ruling on speaking about individuals who abandoned the call to Islam and caused harm, having clear Sharia violations, with the intention of alleviating sorrow and not with the intention of causing harm? Is it permissible to listen to such talk? And is it obligatory for the listener to object to the speaker?

The default rule is that it is impermissible to mention a Muslim with what they dislike, except in exceptional cases: such as seeking a solution to a problem, or the wronged person mentioning their oppressor to the extent of the injustice, or mentioning the Sharia violations of those who openly commit them. If the conversation is merely for venting (فضفضة), then it is impermissible because it is forbidden backbiting. The ruling on listening and disapproving follows the ruling on the speech itself: what is forbidden is impermissible to listen to except for disapproval, and what is permissible has no objection to listening to, nor is disapproval obligatory in it. It is advised to be patient in obedience, in enduring harm for the sake of da'wah, and in refraining from sins like backbiting, which the Sharia warns against.