I have a much, much better idea of what process is using network traffic or other resources on Linux than on Windows (I don't know how often tracing tools point

I have a much, much better idea of what process is using network traffic or other resources on Linux than on Windows (I don't know how often tracing tools pointed fingers at the "system" process for weird magic like CPU or network usage). Unless you mean the 20.04 LTS thing specifically (it sounds like you had this issue for longer), it should be exceedingly easy to turn off anything that runs automatically.