Corrected entry: The whole blackmailing episode is based on Kenny watching illegal underage videos. But "they" recorded Kenny with his own webcam, so how would they know what kind of material he was watching? Sure, they can also record his screen using the virus on the notebook, but then they would have to compose both streamings in a single video, and that would be easily deniable. How do they want to prove he was actually watching that illegal stuff and not something which was added in editing?
San Junipero - S3-E4
Corrected entry: About halfway through the episode Yorkie is seen crossing the road and walking towards a cinema. As the camera pans out a big poster for the movie Scream can be seen on the side of the cinema. This episode is set in 1987, however, Scream wasn't released until 1996.
Correction: You completely missed what was going on. While the episode starts in 1987 and it will say "one week later", Yorkie is traveling through time. After 1987, she's in 1980. Then she's in 1996. Before she crosses the street where we see the "Scream" poster, the TV is playing Alanis Morissette's "Ironic" song and the sign says "New 1996 model."
Correction: You don't need a record a screen to prove that a computer was accessing illegal content. They would have his internet history, names of files and the IP address of his computer, along with the video of him. When this information was passed to the police, they would seize the computer (shown at the end of the episode) and subsequently find the files he had accessed. Additionally, they don't need to send all of this to Kenny, he just has to believe that they have the evidence. That would be enough for him to obey them. Even if the evidence regarding his online activity is not enough for him to be convicted, there is also a video of him murdering a man.