Disable the UI Patterns Source field in Entity Form Display by default
Test translations
Do we need to add messages like Layout builder does: " You are editing the layout template for all Basic page content items. " "You are editing the layout for this Basic page content item. Edit the template for all Basic page content items instead."
UX: Checkbox with a state to show/add the override options? Wording? What else? Check with @mogtofu33
Unlimited vs limited cardinality: do we warn the user some sources positioned at the root may be removed at save? do we prevent the addition?