How can I add a USB Ethernet connection in Linux?
USB ethernet devices will often just work when you plug them in on Linux. You typically do not have to do any additional configuration or install drivers.
On the Raspberry Pi 4, please note that the blue USB ports are USB 3.0 and capable of Gigabit speeds, where the black USB ports are USB 2.0 and have a much lower speed (up to 300Mbps, best case, but often lower).
Once it appears, you can adjust the Connection Settings, such as Priority, to control how Speedify uses the adapter.