A temporary blank white screen appears when add new Post

[abduremon]

After installing WordPress 7, the admin area briefly shows a blank white screen when opening the post editor through Post → Add New.

## Issue
When clicking Add New under Post, the editor page initially shows a completely blank (white screen).

## Reproduction Steps

• Install WordPress 7.
• Log into the WordPress admin dashboard.
• Navigate to Post → Add New.
• Observe the editor loading behavior during the initial page load

## Actual Result
The editor page shows temporarily blank/white before the post editor content appears.

## Expected Result
The post editor should load properly on the first attempt without displaying any temporary blank white screen.

[abduremon]

A temporary blank white screen appears when add new Post

[jorbin]

I believe that this is the view transition and I think this is working as expected. See #64470. @flixos90 and @westonruter, does this look expected to you?

[westonruter]

That looks expected, yes, especially because the editor is in full screen mode, although the admin bar shouldn't go white either.

However, with full screen mode it definitely looks off, because the admin menu also flashes white when it would be expected to persist. See navigate-to-editor-without-fullscreen-mode.mp4​.

This is related to #65032, which also makes improvements to view transitions. For the issue here, the admin menu and admin bar being hidden while the editor loads is surely an issue that needs to be fixed in Gutenberg. Instead of (apparently) hiding the entire body until the editor loads, it should instead be hiding the #wpcontent element only.

[westonruter]

Related: #65309

The new Connectors screen similarly appears to be hidden until it is fully rendered. However, in the case of Connectors the admin bar and admin menu are not hidden during the rendering process.

[khokansardar]

I've opened a Gutenberg PR implementing the approach @westonruter suggested in comment:3 — keeping the admin bar and admin menu painted while the editor loads, so only the empty content area is blank during the cross-document view transition, rather than the whole screen flashing white.

Gutenberg PR: ​https://github.com/WordPress/gutenberg/pull/78834