Highcharts: How to make shared tooltip even when series doesn't have same X value?

In short: I want to make a shared tooltip for the column chart and scatter chart when the scatter chart doesn't have the same "x" values as the column chart.

This is a minimal reproducible example of my problem:

https://jsfiddle.net/Baruch_Levin/wo50t4us/15/

Code:

Highcharts.chart('container', {
    chart: {
        type: 'column'
    },
    xAxis: {
        categories: ['USA', 'China'],
    },
    yAxis:[{}, {
    opposite: true
    }],
    tooltip: {
        shared: true
    },
    series: [
        {
            name: 'Corn',
            data: [406292, 260000],
            yAxis: 0
        },
        {
            name: 'Wheat',
            data: [51086, 136000],
            yAxis: 0
        },
        {
		        name: 'Benchamrk prev year',
            type: "scatter",
            data: [[-.15,1],[.15,3],[.85,4],[1.15,1]],
            yAxis: 1,
        }
    ]
});

I use the scatter plot as a benchmark, to know what was the values in the previous year.
Then I want a shared tooltip that will show me:

USA: {some_value}
USA prev year: {some_value}
China: {some_value}
China prev year: {some value}

Then I want that also in hover, the column chart AND the scatter plot will be selected.

How can I do that?

I saw this question:
https://stackoverflow.com/questions/46093144/highcharts-shared-tooltip-for-non-matching-x-values

But it doesn't help me, because the jsfiddle there doesn't show how to select on hover both series points etc'
And I am not sure "interpolation" is the right solution, and it was in 2017, maybe now there is another solution...

Thanks in advance!

To accomplish this, apply the tooltip.formatter with the calculations as follows:

tooltip: {
    shared: true,
    formatter() {
      let category = this.key,
        tooltipText = '',
        a = [],
        b = [];

      this.series.chart.series.forEach(series => {
        let seriesName = series.name;
        series.points.forEach(point => {
          if (point.category === category || point.category < (this.point.x + 0.5) && point.category > (this.point.x - 0.5)) {

            if (typeof point.category !== 'number') {
              a.push(`<span>${point.category}: ${seriesName}: ${point.y}</span></br>`);
            }
            if (typeof point.category === 'number') {
              b.push(`<span>${point.series.name}: ${point.y}</span></br>`);
            }
          }
        })
      });

      for (let i = 0; i < a.length; i++) {
        tooltipText += `${a[i]} ${b[i]}`
      }
      return tooltipText;
        }
      },

Additionally, to remove opacity, it will be necessary to modify series.states

   plotOptions: {
    series: {
      states: {
        inactive: {
          opacity: 1
        },
        hover: {
          enabled: false
        }
      }
    }
  },

Demo:
https://jsfiddle.net/BlackLabel/5vdnmrtw/

API References:
https://api.highcharts.com/highcharts/tooltip.formatter
https://api.highcharts.com/highcharts/plotOptions.series.states