macOS background processes that use the network

Read the group headings as advice, not instructions. "Optional" means the feature is not required for macOS to work — it does not mean you will not miss it. rapportd, for example, is what powers Handoff, Universal Clipboard and Sidecar; plenty of people use those every day. Find out what a process actually does before deciding it is expendable.

Where you turn something off matters. If macOS has a setting for the feature, use that setting — the work is then never queued, which is cleaner and more predictable than letting it start and blocking it at the network layer. Each page below names the System Settings location where one exists. Blocking with a tool like Bytetally is the fallback for the cases where Apple exposes no switch, or where you want the feature most of the time and only need to rein it in on a metered connection.