Checkboxes are used for toggling between states. Instead of binding to input.value, we bind to input.checked:
App
<input type="checkbox" bind:checked={yes}>previous next
<script>
let yes = $state(false);
</script>
<label>
<input type="checkbox" checked={yes} />
Yes! Send me regular email spam
</label>
{#if yes}
<p>
Thank you. We will bombard your inbox and sell
your personal details.
</p>
{:else}
<p>
You must opt in to continue. If you're not
paying, you're the product.
</p>
{/if}
<button disabled={!yes}>Subscribe</button>
