Block widgets in the Customizer, enhancements to the Site Editor, improvements to rich text placeholders, are included in Gutenberg 10.4.
One of the aims of the Block-based Widget Editor project is to support block widgets in the Customizer, and Gutenberg 10.4 is the first version to do so.
The Site Editor List View has included multiple design improvements in version 10.4, including more consistent icon size and spacing, as well as new colours for hover, focus, and select states. The site icon and name have been added to the publishing UI, giving it a more personal touch while also making it more clear for full-screen or smartphone users.
Rich text block placeholders have been tweaked in this update to enhance the editing experience. Beginning with Gutenberg 10.4, rich text blocks will display a shorter placeholder text that will remain visible even when the block is focused.
Source: Make WordPress Core