Different Ethernets: how to prefer certain network

I was using my computer normally, transferring lots of data due to YouTube usage etc. Suddenly my mobile network operator sends a text message saying I have used over 25 GB per this month. I was surprised. Then I realized that as soon as I had connected my iPhone to my computer (just to charge it), Windows 10 had started using the phone's network. So I found out that Windows 10 Settings / Data usage has "Ethernet" and "Ethernet 4". Also, Ethernet (above Data usage) has "Network" and "Network 3". Very confusing. Apparently "Network 3" is effectively the same as "Ethernet 4".

When I hover mouse cursor on top of systray's network icon, it says "Network" and "Network 3" as if they would be both actively used at the same time, but that's not possible is it?

How do I even see which "Ethernet" or "Network" is actually being used?

How do I force (reliably) a particular Ethernet to be preferred?

I noticed I can disable a certain network "completely" in Control Panel > Network and Internet > Network and Sharing Center > Change adapter settings. However, I'm not sure if the connection might still spontaneously turn on after updates etc. So it would be important that the preferred connection is the real Ethernet, not a mobile connection.

(I don't want to solve this by disabling tethering in my iPhone, because that also disables other tethering which I don't want. Also the Data limit in Windows Settings does nothing useful, apparently it only warns in the notification center.)

Thank you, that Automatic metric value thing seems to be exactly what is needed to customize the priority for the network connection.

I noticed that I can go to systray's network icon > Open Network & Internet settings > Network and Sharing Center, where you can see the "Network" connections. And at right, it shows e.g. "Ethernet" and "Ethernet 4". By clicking those, I can see realtime Sent/Received bytes. So this gives me insight as to which connection is actually being used. However, now that I look at it, while connected both to ethernet and mobile, on BOTH connections the Bytes Sent/Received are increasing. However, only the otherone increases substantially, if I watch YouTube for example. The other one seems to be only doing minimal traffic. Seemingly the other one is therefore preferred but the second connection is still connected also. What does this secondary connection do in this case? What does the small traffic consist of?

Is it impossible to use two connections simultaneously in this setup (to speed up Internet)?