Chartjs-Use chartjs-plugin-annotation 0.5.7 in Charts 2.9.x with React

It looks like you are trying to implement the annotations plugin as if you would integrate it to a current chart.js version. E.g. your define your annotations in plugins.

This is an example that works with the given versions. Please note that I added the annotation object right away in options what gives the wanted annotation. (In my example in form of a red line.)

import React, { useEffect, useRef } from "react";
import Chart from "chart.js";
import annotationPlugin from "chartjs-plugin-annotation";

Chart.pluginService.register(annotationPlugin);

const LineGraph = () => {
  const chartRef = useRef(null);

  useEffect(() => {
    if (chartRef?.current) {
      const chartToDraw = chartRef.current.getContext("2d");

      new Chart(chartToDraw, {
        type: "line",
        data: {
          labels: ["Jan", "Feb", "March"],
          datasets: [
            {
              label: "Sales",
              data: [86, 67, 91]
            }
          ]
        },
        options: {
          annotation: {
            drawTime: "afterDatasetsDraw", // (default)
            events: ["click"],
            dblClickSpeed: 350, // ms (default)
            annotations: [
              {
                drawTime: "afterDraw",
                id: "a-line-1",
                type: "line",
                mode: "horizontal",
                scaleID: "y-axis-0",
                value: "25",
                borderColor: "red",
                borderWidth: 2
              }
            ]
          }
        }
      });
    }
  }, []);

  return (
    <div className={{ width: "100%", height: 500 }}>
      <canvas id="myChart" ref={chartRef} />
    </div>
  );
};

export default LineGraph;

You can see it working here:
https://codesandbox.io/s/chart-js-2-9-4-annotation-example-f3h7d?file=/src/LineGraph.js

Chart.js plugin annotation documentation for 0.5.7:
https://www.chartjs.org/chartjs-plugin-annotation/0.5.7/