Google-sheets – Chart only rows with “x”

This is an excellent time to use a pivot table.

Select columns B and C, then click on Data → Pivot table...

In the Pivot table editor sidebar on the right side:

• In the Columns section, add the Category field. Uncheck Show totals if you do not want the Grand Total column.
• In the Values section, add the Category field and summarize by COUNTA.

Now select the pivot table data on the sheet and click on Insert → Chart. Select Column chart for the Chart type.

New form submissions will update the pivot table and the updated pivot table will update the chart. This is what the pivot table and chart look like using the example data you provided in your question:

Copy of a more extreme example of 'co-linearity`:

seems to have pointed to an acceptable solution/workaround. That is, add data point markers (Point size, in Customise in Chart Editor) - in the image to one [red] data series (also with the line made thinner than the default and the other [blue] series line increased in width).