Why are you using this in an arrow function?

Try this:

import React from "react";
import ReactPlayer from "react-player";

let player;

export const VideoPlayer = ({
  endVideo,
  timePlayed,
  controls,
  playing,
  videoDuration
}) => (
  <div className="video-player">
    <ReactPlayer
      ref={(ref) => {
        player = ref;
      }}
      url="https://res.cloudinary.com/amarachi-2812/video/upload/v1630370229/videoplayback_1_pr2hzi.mp4"
      playing={playing}
      // playing={true}
      controls={controls}
      onStart={() => player.seekTo(timePlayed)}
      onEnded={endVideo}
    />
  </div>
);

export const MemoizedVideoPlayer = React.memo(VideoPlayer);

Try, set instance with help useState hook.

Wrap the handlers in useCallback to prevent unnecessary re-render, but don't forget about their dependencies if they appear.

Do not forget to look at the repository of the libraries you are using, sometimes it helps.

Also, my advice is to read about functions in more detail.

Additionally, I made a few small changes.

• The component is named video player. The property of "videoDuration" can be called "duration". This will be more correct and we will not lose in understanding the transferred properties.
• Url would get from props. To point the source outside and the component was reused.
• Renamed the "endVideo" property to "onEnded". For clarity, that is, it will be named similarly to the handler to which we transfer to the react-player

Let's start!

import React, { useState, useCallback } from "react";
import ReactPlayer from "react-player";

export const VideoPlayer = ({ url, onEnded, timePlayed, controls, playing, duration}) => {
 const [instance, setInstance] = useState(null);

 const handleStart = useCallback(() => {
     if (instance) {
         instance.seekTo(timePlayed)
     }
 }, [instance, timePlayed])

 return (
    <div className="video-player">
        <ReactPlayer
            ref={setInstance}
            url={url}
            playing={playing}
            controls={controls}
            onStart={handleStart}
            onEnded={onEnded}
        />
    </div>
)};