Since you asked specifically about things like misinformation and propaganda, which I'm interpreting as people misusing a decentralized global system, I will omit critiques which are simply about the "power of large, evil computers." But we're still looking at a very big realm of dystopia, which even predates the actual formation of the Internet. Even before the Internet, some people had concerns about the general concept of networked computers and the people creating the networking.

An early critique of globalized, networked automation can be found in The Machine Stops, a 1909 short story by E. M. Forster. The story basically a future world in which all human beings are isolated from each other, interacting only through video link (basically, Zoom calls) and all food and products are delivered to one's home by an automated computer network called the Machine, which also provides utilities and climate control. Even music is no longer stored on physical disks but is only accessible through a streaming service provided by the Machine. Humanity lives underground due to having destroyed the earth's surface with pollution. The story explores several dystopian aspects of this scenario including the impact of such a sedentary existence on the human body and the issue of complete reliance on the network.

Much later, the cyberpunk genre which developed in tandem with the Internet itself was sometimes quite laudatory of the potential of the new network to liberate people from dystopian situations, as seen in the works of Neal Stephenson and William Gibson, but other writers were more skeptical. The first cyberpunk novel, The Shockwave Rider by John Brunner (1975) is a good example: the network in this book is shown to hold a great deal of information about each American citizen, which is prone to hacking or theft as well as surveillance possibilities, and most people live with a feeling of resignation that they are slaves to the data on the network. This is something that was beginning to actually happen in the 1970s and had previously been predicted by the cybernetics pioneer Norbert Wiener in 1948, but Weiner didn't specifically talk about decentralized computer networking, more about supercomputers. In fact, while computer control is portrayed as evil in The Shockwave Rider, the network aspect is portrayed as good, as the code can receive unauthorized improvements from a skilled hacker.

Some aspects of the Internet were noticed and expanded by early participants. Ender's Game (1985) famously has a subplot that's all about using fake arguments on a pseudonymous social media site to generate massively successful propaganda during a war, and Vernor Vinge's influential 1981 story "True Names" is about the related phenomenon of doxxing. In 1990, Julian Dibbell wrote "A Rape in Cyberspace" describing how a troll engaged in nonconsensual roleplaying in an early chatroom, and pointed out that while this was just "free expression" on the egalitarian, democratic platform of the Internet, it was interpreted by most chatroom users as emotional abuse and grounds for banning; basically, an early look at how "free expression" could be disruptive and require moderation or other intervention.

In 1995, two British theorists wrote a manifesto called "The Californian Ideology" which argued that Silicon Valley elites were using the Internet to escape government regulation and create virtual domains in which they themselves would control social networking and economic power, becoming in essence a new ruling caste in the Internet world. It amounts to a prediction of Facebook and Bitcoin. This brings us close enough to the 20-year mark that I'll stop here but I bet there were some great dystopian predictions between 1995 and 2002 that I'm missing.