Widget screen: Custom block styles are not available when running WP 5.7

[carolinan]

Describe the bug
When a block with a custom block style (register_block_style) is added to a widget area,
the custom style is not present in the block inserter or block sidebar.

To reproduce
Steps to reproduce the behavior:

1. Activate Gutenberg
2. Activate a theme with custom block styles, for example Seedlet.
3. In the widgets screen, place a block that has a custom block style, for example, latest posts in Seedlet.
4. When adding the block, see that the block style is not showing in the block inserter.
5. With the block selected, open the block sidebar, and view the styles section.
6. See that the custom styles are missing, or if it is the only style, that the styles section is missing.

Expected behavior
I expect all options to be available when placing the block.

Editor version (please complete the following information):

• WordPress version: 5.5.1
  -Gutenberg version 9.1

[draganescu]

I was able to reproduce this on Gutenberg master as of Oct. 17th.

[talldan]

I can also replicate using seedlet. What's interesting is that from the console this still works:

wp.blocks.registerBlockStyle( 'core/latest-posts', {
    name: 'fancy-latest-posts',
    label: 'Fancy Latest Posts',
} );

[noisysocks]

Thanks for the report! I can only reproduce it when running the Gutenberg plugin on WP 5.7. It's fixed in 5.8-alpha. Going to de-prioritse the issue in the Widgets project board.

[draganescu]

If it's fixed in 5.8-alpha why not close this issue?

[carolinan]

I can confirm that this is fixed. I don't believe there are any backporting to 5.7 concerns, as far as I know, that is not planned.
I am not sure why it is listed in maybe later. Please reopen if needed.