This example uses OpenLayers v10.9.0. The latest is v.
Edit

#### Tile Load Events

tile 10 events 3 loading 8

#####

Example using tile load events.

Image tile sources fire events related to tile loading. You can listen for `tileloadstart`, `tileloadend`, and `tileloaderror` type events to monitor tile loading progress. This example registers listeners for these events and renders a tile loading progress bar at the bottom of the map. The progress bar is shown and hidden according to the map's `loadstart` and `loadend` events.

##### main.js

    import Map from 'ol/Map.js';
    import View from 'ol/View.js';
    import TileLayer from 'ol/layer/Tile.js';
    import ImageTile from 'ol/source/ImageTile.js';

    /**
     * Renders a progress bar.
     * @param {HTMLElement} el The target element.
     * @class
     */
    function Progress(el) {
      this.el = el;
      this.loading = 0;
      this.loaded = 0;
    }

    /**
     * Increment the count of loading tiles.
     */
    Progress.prototype.addLoading = function () {
      ++this.loading;
      this.update();
    };

    /**
     * Increment the count of loaded tiles.
     */
    Progress.prototype.addLoaded = function () {
      ++this.loaded;
      this.update();
    };

    /**
     * Update the progress bar.
     */
    Progress.prototype.update = function () {
      const width = ((this.loaded / this.loading) * 100).toFixed(1) + '%';
      this.el.style.width = width;
    };

    /**
     * Show the progress bar.
     */
    Progress.prototype.show = function () {
      this.el.style.visibility = 'visible';
    };

    /**
     * Hide the progress bar.
     */
    Progress.prototype.hide = function () {
      const style = this.el.style;
      setTimeout(function () {
        style.visibility = 'hidden';
        style.width = '0px';
      }, 250);
    };

    const progress = new Progress(document.getElementById('progress'));

    const key = 'get_your_own_D6rA4zTHduk6KOKTXzGB';
    const attributions =
      '<a href="https://www.maptiler.com/copyright/" target="_blank">&copy; MapTiler</a> ' +
      '<a href="https://www.openstreetmap.org/copyright" target="_blank">&copy; OpenStreetMap contributors</a>';

    const source = new ImageTile({
      attributions: attributions,
      url: 'https://api.maptiler.com/maps/streets-v2/{z}/{x}/{y}.png?key=' + key,
      tileSize: 512,
    });

    source.on('tileloadstart', function () {
      progress.addLoading();
    });
    source.on(['tileloadend', 'tileloaderror'], function () {
      progress.addLoaded();
    });

    const map = new Map({
      layers: [new TileLayer({source: source})],
      target: 'map',
      view: new View({
        center: [0, 0],
        zoom: 2,
      }),
    });

    map.on('loadstart', function () {
      progress.show();
    });
    map.on('loadend', function () {
      progress.hide();
    });

##### index.html

    <!DOCTYPE html>
    <html lang="en">
      <head>
        <meta charset="UTF-8">
        <title>Tile Load Events</title>
        <link rel="stylesheet" href="node_modules/ol/ol.css">
        <style>
          .map {
            width: 100%;
            height: 400px;
          }
          .map {
            background: #85ccf9;
          }
          .wrapper {
            position: relative;
          }
          #progress {
            position: absolute;
            bottom: 0;
            left: 0;
            height: 0;
            box-shadow: 0px 0px 1px 2px rgb(255,204,0);
            width: 0;
            transition: width 250ms;
          }
        </style>
      </head>
      <body>
        <div class="wrapper">
          <div id="map" class="map"></div>
          <div id="progress"></div>
        </div>

        <script type="module" src="main.js"></script>
      </body>
    </html>

##### package.json

    {
      "name": "tile-load-events",
      "dependencies": {
        "ol": "10.9.0"
      },
      "devDependencies": {
        "vite": "^3.2.3"
      },
      "scripts": {
        "start": "vite",
        "build": "vite build"
      }
    }