Trying to validate this myself for Dark Reader without breaking out Wireshark and monitoring some big tech site while I toggle color modes (which I might do later if I think of it and find the time)

You would also need to setup up a custom certificate authority to MITM the TLS traffic (a very blunt wording but to the point).
I think you should be fine using the network tab in the normal browser devtools, or the one in the browser toolbox as that latter one is supposed to show all traffic your browser makes.