It is a common use case to make sure a preview of an ACF block does appear in the editor. This may be for many reasons - e.g. complex blocks that only work in certain contexts, or simply because it results in a large output and makes it harder for admin to edit. This has been enforceable by using mode:edit and support {mode:false} - and potentially not including preview CSS in the back-end at all.

When clients upgrade to WP 7 and the iframe is enforced, undesired previews will start appearing for these blocks, resulting in a huge visual (and often broken layout) change. This was already noticed before ACF v3 blocks were released, e.g. when people started noticing unwanted previews when editing block patterns.

I have been resolving this when developing ACF v3 blocks by adding code like this to the top of every block:

```if ($is_preview) {

?>

<div class="customblockpreview">

<p><?php echo $block['title']; ?> block</p>

<p>Click pencil icon to edit.</p>

</div>

<?php

return;

}```

and just styling this to be a plain bordered box in the editor.

However, I have developed many, many sites in the past with custom ACF blocks where this code won't be in place.

Can you consider adding something similar by default - adding a preview-less option for v3 blocks, and then applying this by default if the deprecated mode:edit setting was applied? This will result in a much similar experience to what people are used to, vs repeated error reports upgrading to WP 7.