block.json - custom block style asset is loaded unconditionally to all pages with a non block-based theme

[incrediblewp]

Wordpress version: 6.6.1.
Description:
When using the block.json method to register a custom block and a regular theme is being used (not a block-based theme), the block style asset is loaded even when the block is not being used. When switching to a block-based theme the block style asset is loaded conditionally.

[poena]

Hi @incrediblewp

This difference between block themes and classic themes is a known limitation, this post explains it better than I can:
​https://make.wordpress.org/core/2021/07/01/block-styles-loading-enhancements-in-wordpress-5-8/

In short, in classic themes the styles need to be added to the footer, after the blocks have rendered. And because this can change the loading order of the CSS, breaking the style of existing themes, it was decided to not load the styles conditionally by default in classic themes.

Theme developers can opt-in to loading the styles conditionally.