As far as I know you can set any connection, wired or wireless, to be considered metered by Windows 10.
There are now a lot of wireless internet services that allow you to connect a desktop (or laptop, for that matter) to the wireless modem-router via ethernet. There most often are data caps on those services, so you can still declare that your wired connection is a metered connection.
Brian AKA Bri the Tech Guy (my website address is in my profile) Windows 10 Home, 64-bit, Version 1709, Build 16299
Here is a test to find out whether your mission in life is complete. If you’re alive, it isn’t.
~ Lauren Bacall