Extracted from #70743

What problem does this address?

We plan to have the post editor function entirely as an iframe in the future. Also, to maintain backward compatibility and allow developers to verify in advance whether their blocks will work within an iframe, the post editor will only function as an iframe if all block versions are 3.

However, as reported in #70743, there appear to be some technical issues with making blocks work within an iframe. Please refer to this comment for an example: #70743 (comment)

What is your proposed solution?

To assist developers in migrating to Block API version 3, we will create a technical migration guide. I think we can create content based on the content of these posts.

• Blocks in an iframed (template) editor – Make WordPress Core
• Preparing the Post Editor for Full iframe Integration – Make WordPress Core