Is it permissible to talk about events that happened to other people with the aim of self-entertainment and sharing worries, and is that considered backbiting, knowing that these events are real and concern the speaker?

Backbiting is your mention of your brother in his absence with what he dislikes. If you speak about a person with matters specific to them that do not involve disparagement or revealing their private affairs, then that is not backbiting. However, if these matters were forbidden acts that they committed, it is not permissible to mention them because it is a forbidden public disclosure [of sins]. But if they were permissible matters intended for recreation, then it is permissible, with the caveat that one should not excessively engage in useless talk.