The steady low line to the left of the graph is it using the “local network” from my computer (didn’t even know it had one) and it goes straight up when I interrupt it and tell to switch to the WiFi for download. And it keeps doing it so I have to switch the the WiFi manually every time. Why is that so and is there a way to “always use WiFi?”
You most probably have a normal pc/laptop that’s connected to the internet and with steam (and your games) installed. This means that steam doesn’t access their servers to download a game but instead copies the files from your other pc to the deck. This is usually faster and doesn’t really use your internet connection.