Try to change style in current month in chartJS

I think it does not matter if you work with angular as it is a chart.js thing.
Check how you can configure the ticks (axis values are called ticks) here.

Find this code modification to configure each of the ticks:

const config = {
  type: 'line',
  data: data,
  options: {
    responsive: true,
    plugins: {
      title: {
        display: true,
        text: 'Chart with Tick Configuration'
      }
    },
    scales: {
      x: {
        ticks: {
          // For a category axis, the val is the index so the lookup via getLabelForValue is needed
          callback: function(val, index) {
            // Hide the label of every 2nd dataset
            return index % 2 === 0 ? this.getLabelForValue(val) : '';
          },
          color: 'red',
          font: {
            weight: (w) => { //4th x axis index will be bold
              return w.index === 4 ? '900' : 'normal'; 
            }
          }
        }
      }
    }
  },
};

You can paste that right there in the documentation page and check how it works.
To choose the degree of boldness you like, give lookd to the documentaion. It is the weight property the one you need to set.

Edit:

Find the 4th x tick bolded: