Edit in JSFiddle

const editor = grapesjs.init({
  container: '#gjs',
  fromElement: true,
  height: '100%',
  storageManager: false,
  noticeOnUnload: false,
  plugins: ['gjs-blocks-basic'],
  assetManager: {
    custom: true,
    assets: [
      'https://via.placeholder.com/350x250/78c5d6/fff/image1.jpg',
      'https://via.placeholder.com/350x250/459ba8/fff/image2.jpg',
      'https://via.placeholder.com/350x250/79c267/fff/image3.jpg',
      'https://via.placeholder.com/350x250/c5d647/fff/image4.jpg',
      'https://via.placeholder.com/350x250/f28c33/fff/image5.jpg',
      'https://via.placeholder.com/350x250/e868a2/fff/image6.jpg',
      'https://via.placeholder.com/350x250/cc4360/fff/image7.jpg',
    ],
  },
});

const pagesApp = new Vue({
  el: '.assets-wrp',
  data: { assets: [] },
  mounted() {
    editor.on('asset:custom', this.handleAssets);
  },
  destroyed() {
    editor.off('asset:custom', this.handleAssets);
  },
  methods: {
    handleAssets(props) {
      props.container.appendChild(this.$el);
      this.assets = props.assets;
      this.select = props.select;
      this.remove = props.remove;
    },
  }
});

<div id="gjs">
  <div style="padding: 25px">Double click on the image below to open the custom Asset Manager</div>
  <img src="https://via.placeholder.com/350x250/78c5d6/fff/image1.jpg" />
</div>

<div style="display: none;">
  <!-- Vue app for assets -->
  <div class="assets-wrp">
    <div class="assets">
      <div v-for="asset in assets" :key="asset.getSrc()" class="asset" @click="select(asset)" @dblclick="select(asset, true)">
        <img class="asset-img" :src="asset.getSrc()" />
        <div class="asset-over">
          <div>Select</div>
          <div class="asset-name">{{ asset.getFilename() }}</div>
        </div>
        <div class="asset-remove" @click.stop="remove(asset)">Remove</div>
      </div>
    </div>
  </div>
</div>

body, html {
  margin: 0;
  height: 100%;
}

.assets-wrp {
  margin-top: 15px;
  min-height: 300px;
}
.asset-img {
  max-width: 100%;
  display: block;
}
.asset {
  width: 16.66%;
  height: 90px;
  overflow: hidden;
  border-radius: 5px;
  margin-bottom: 20px;
  cursor: pointer;
  position: relative;
}
.assets {
  display: flex;
  flex-wrap: wrap;
  gap: 4.15%;
}
.asset-over {
  position: absolute;
  width: 100%;
  height: 100%;
  opacity: 0;
  top: 0;
  left: 0;
  background-color: rgb(0 0 0 / 70%);
  transition: opacity 0.3s ease-in-out;
  display: flex;
  justify-content: flex-end;
  align-items: center;
  font-size: 12px;
  flex-direction: column;
}
.asset-remove {
  position: absolute;
  top: 0;
  right: 0;
  padding: 5px;
  font-size: 12px;
  opacity: 0;
  transition: opacity 0.3s ease-in-out;
}
.asset-name {
  margin-bottom: 10px;
}
.asset:hover .asset-over,
.asset:hover .asset-remove {
  opacity: 1;
}