Layout Builder translation locks Paragraphs field inside custom block configuration

Problem/Motivation

Steps to reproduce

1. Install Drupal 11.3.2
2. Enable modules:
3. Core: Language, Content Translation, Layout Builder
4. Core: Layout Builder translation (layout_translation)
5. Contrib: Paragraphs, Entity Reference Revisions
6. Add 2 languages:
7. Default language: Dutch (nl)
8. Additional language: English (en)
9. Create a Paragraph type named Links with fields:
10. field_link (Link)
11. field_button_color (List text) (optional)
12. Enable translation for the Paragraph type (Translate paragraphs type tab) and mark the fields as translatable.
13. Create a custom block type named Title Text Link with fields:
14. field_title (Text)
15. body (Formatted long text)
16. field_multi_link (Entity reference revisions → Paragraph type: Links)
17. Enable translation for the custom block type.
18. The Paragraph reference field (field_multi_link, entity_reference_revisions) is shown as “unsupported” in translation settings and cannot be marked translatable.
19. Create a Content type (example: Basic page) and enable Layout Builder for it.
20. Enable Content translation for the content type and enable Layout translation.
21. Create a node in Dutch (default language).
22. Open Layout Builder for the node and add the custom block Title Text Link.
23. In the Layout Builder sidebar, fill Title/Body and add items in the Link → Links paragraph reference field.
24. Save the layout.
25. Translate the node to English and edit the English layout translation.
26. Try to edit the same block in the English layout translation.

Actual result

Inside the Layout Builder block configuration (sidebar), the paragraph reference field (field_multi_link) becomes locked in the translation. The UI shows a lock icon and the paragraph items cannot be edited for the translated language.
This happens even though:

1. Paragraph fields are configured as translatable
2. Layout translation is enabled
3. Block type fields are configured as translatable

Proposed resolution

Remaining tasks

User interface changes

Introduced terminology

API changes

Data model changes

Release notes snippet