Unable to change the lightbox settings of the Image block within Global Styles when KSES is active

[mmtr]

Description

The KSES filters don't allow to change the lightbox settings of the block image via the Global Styles sidebar in the site editor.

These filters are only registered when a user doesn't have the unfiltered_html capability (which is the case for multisite regular admins).

When these filters are active, any change to the lightbox settings is reverted back to its previous value.

Step-by-step reproduction instructions

1. Enable the KSES filters with add_action( 'init', 'kses_init_filters' );
2. Go to Appearance > Editor
3. Open the Styles sidebar
4. Select "Blocks"
5. Select "Image"
6. Change the "Enlarge on click" options
7. Save the changes
8. ⚠️ Note how the changes are reverted

Screenshots, screen recording, code snippet

Screen.Recording.2025-11-11.at.12.40.17.mov

Environment info

• WordPress: 6.8.3
• Gutenberg: 22.0.0
• Theme: Twenty Twenty-Four 1.3

Please confirm that you have searched existing issues in the repo.

• Yes

Please confirm that you have tested with all plugins deactivated except Gutenberg.

• Yes

Please confirm which theme type you used for testing.

• Block
• Classic
• Hybrid (e.g. classic with theme.json)
• Not sure

[mmtr]

cc @oandregal @andrewserong @ramonjd @youknowriad

I think this has been a problem since the feature was introduced in #54509

[oandregal]

cc @michalczaplinski

[ramonjd]

Looking at theme.json schema, all settings are allowed in blocks. So I'm wondering if this is a larger bug, where all non-preset settings are stripped in blocks when kses_init_filters is active.

[ramonjd]

Found this small bug while testing as well:

• Image block: set img_srcset to avoid PHP undefined var warning #73453