It is a common use case to make sure a preview of an ACF block does not 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.