2:1 Rib knitting is effectively alternating between 2 wales of single jersey on the front bed and 1 wales of single jersey on the back bed, but it's not as simple as the 1:1 or the 2:2. If we did that (2 knits in the front bed, one knit in the rear bed) the back side of the knit would look very different than the front. To avoid that, the structure of the 2:1 looks like this:
1. Knit front
2. Knit both
3. Knit rear
It is necessary to rack the needle bed by 0.5 because some of the needles in use are directly opposite to each other. This means there is a risk of colliding needles.
Then, open the stitch selector in the toolbar on the left, and select "knit both".
Select the line drawing tool and draw wales alternating between "Knit front", "knit both" and "Knit rear"rear like in the video.
Below a detail of 2:1 rib knitting.