How to show Chart for itemstates switchitem ON/OFF in a page

Add-ons UIs
2

Charting ON/OFF items differs from a “normal” oh-time-series. You need to add a markArea to the chart:
In your code, change the type to line
Replace item: xxxx with:

        markArea:
          - component: oh-mark-area
            config:
              item: status_anwesend
              name: yyyy

For more disucssion about charts of switches have alook at this thread: OH3: Charts/Graphs/Plots - #17 by spy0r