The rating is only available if you are connected to a network (I need this as a point of reference). You also only see the rating if you view the same band (2.4 or 5 GHz) to which you are currently connected to, otherwise it tells you the rating is not available.
There are three different views to get channel recommendations. With "Arrow up" you can expand it. To set it back to normal/minimized you can ether press "Arrow down" or the "Back-Button" on mobile. You can also get it out of the way by pressing "Minimize" and then back to normal by pressing "Show".
This is the rating pane in normal view below the graph. You see the recommend rating only. The accent color simply indicates the rating your current channel has and the rest is the improvement you can get.
This is the rating minimized. In case you don't see the star, you have to enable this first. Therefore go to "View" (the eye icon) and then set "Better channel" with a check mark. This entry will only be shown when the rating pane is minimized (because only then you can see the star).
This is the rating pane expanded. You see the recommend rating and the ones every channel gets individually. The accent colored one simply indicates the channel to which you are connected to and in the recommend section it is the rating your current channel has and the rest is the improvement you can get by changing to this channel.