<div class="example">
  <button id="writeCB">Write "Hello, World!" to Clipboard</button>
  <textarea id="testDump" placeholder="Use this textarea to test pasting"></textarea>
  <p>If this doesn't work for you <a href="https://codepen.io/pen/debug/xxojZOL" target="_blank">try Debug Mode</a>.</p>
</div>

body {
  height: 100vh;
  margin: 0;
  display: grid;
  place-items: center;
  background: #455a64;
  font-family: monospace;
}

.example {
  background: white;
  border-radius: 12px;
  overflow: clip;
  width: 75dvi;
  display: grid;
  padding: 1rem;
  gap: 1rem;
}
textarea {
  width: 100%;
  height: 100px;
}

p {
  text-align: center;
  padding-inline: 1rem;
}

document.querySelector("#writeCB").addEventListener("click", async () => {
  await navigator.clipboard.writeText("Hello World!");
  console.log("Done!");
});