[Solved]-How to show horizontal line instead of a dot for a single value data in highcharts-Highcharts

instead of adding a series with single values, use plot lines:

    xaxis: {
        plotlines: [{
            value: 2010,
            color: 'blue'
        }],
        ...
    }

live demo: https://jsfiddle.net/blacklabel/3654z2yw/

api reference: https://api.highcharts.com/highcharts/xaxis.plotlines