Basically the title. A friend of mine very gravely explained to me that this secret society never actually ended. In fact that they still operate to this day putting symbols of their organization in the media and on buildings to "flaunt their power and only those who are awake can see." She proceeded to show me examples of their "satanic" symbols across different mediums. These symbols appeared to be taken grossly out of context or blatantly misinterpreted to fit the "all powerful satanic secret society narrative." Upon trying to explain to her the arbitrariness of symbolism and point out some of the logically fallacious reasoning, I was promptly shut down.
Looking into this Bavarian society's history myself, I haven't been able to find any reliable sources that indicate they did any of the things she claims they still do today. And nothing to indicate they were at all satanic or connected to black magic. In fact from what I have found so far they were not religious.
So what is the actual history of the Illuminati? Any reliable/in-depth documentation of their history?
There appear to be two waves of the Illuminati's popularity. The first has been addressed by /u/monjoe in a previous answer. In short, the Illuminati itself was a very short-lived Masonic club, like the Shriners but less successful. After the French Revolution, it was alleged that the Bavarian Illuminati and other Freemasons had engaged in a conspiracy to destroy France.
According to the 2003 biography The Prankster and the Conspiracy: The Story of Kerry Thornley and How He Met Oswald and Inspired the Counterculture as well as the 2021 Adam Curtis documentary Can't Get You Out of My Head, the eccentric libertarian Kerry Thornley, a friend of Lee Harvey Oswald, was angry after being accused of being part of the JFK assassination conspiracy, and invented "Operation Mindfuck", a plan to purposefully make conspiracies sound more ludicrous. One of his plans was to tie every single conspiracy together into a mega-conspiracy headed by the Bavarian Illuminati, which he thought would sound especially silly because the Illuminati had not existed since the 1770s.
The Illuminati joke was taken up by Thornley's friend Robert Anton Wilson, who wrote a series of entertaining sci-fi novels in which the Illuminati create nonexistent conspiracies and fill their own work with red herrings in order to make conspiracy theorists look ridiculous. I am not aware that anyone has written up the full story of how the Illuminati story began to be taken seriously by conspiracy theorists but it began very quickly: Robert Anton Wilson's books came out in 1975 and the far-right Christian John Todd began seriously proposing the existence of an Illuminati in 1977. It is well-known that Wilson's novels were misinterpreted by at least one mentally ill person: Kenneth Lamar Noid, who took hostages at a Domino's because he believed that their mascot "The Noid" was mocking him, and demanded a copy of one of Wilson's Illuminati books in exchange for one of the hostages.