I knew that it was possible to spy on CRT displays due to the signals they radiate, but apparently that is a problem with HDMI too.

Here a very interesting write up on how to extract frames from leaked RF from HDMI cables and using said RF to transmit a webcam stream even: https://www.windytan.com/2023/02/using-hdmi-radio-interference-for-high.html

Here a example of someone using HDMI RF to transmit LoRa signals: https://www.youtube.com/watch?v=HDbdAZd6cLw

This makes for a interesting attack vector for locating a user, if said user clicks on a video (or even a gif) that crafts LoRa frames to radiate from his HDMI and there is for example a Meshtastic receiver near by that relays those frames into a wider network.

There are ways to migrate this issue, for example using the encrypted version of HDMI usually used to enforce content copyright protection, or using a fiber optic HDMI cable (by now they are almost as cheap as the copper ones and are not restricted to a max lenght of 5m).