Thanks for the continued discussion. A few things to add.
@iskis: for the compatibility plugin, we would point to our official one rather than a third-party: https://github.com/AdvancedCustomFields/acf-blocks-v2-iframe-compatibility. It is a temporary bridge while you plan migration, not a long-term fix, but it is the supported option.
For those migrating to V3 and wanting to replicate the old “always in edit mode” experience, @jnicol is on the right track. You can go further with a couple of additional options:
In block.json, adding “renderPreview”: false to the “acf” key shows a clean placeholder with an “Edit Block” button that opens the Expanded Editor, bypassing the preview entirely.
You can also prevent fields from ever appearing in the narrow WP sidebar by setting “hideFieldsInSidebar”: true, so all editing happens in the Expanded Editor only.
If you are registering via PHP rather than block.json, the equivalent options are render_preview and hide_fields_in_sidebar (underscores instead of camelCase).
Full configuration options: https://www.advancedcustomfields.com/resources/acf-block-configuration-via-block-json/
Full release post for 6.8.9: https://www.advancedcustomfields.com/blog/acf-6-8-9-released/
