Second screen is detected by OSX but isn't turned on
Multiple monitors connected as your by DisplayPort (and/or HDMI converted from DisplayPort) served by a USB-C dock won't work on macOS. It will work on Windows, which is what Lenovo advertises.

For macOS you'll need a Thunderbolt dock instead to be able to do this.

A different solution is to plug one monitor into the dock, and the other monitor into the Mac. However you'll need to connect two cables to the computer this way, which is probably what you want to avoid when using a dock.