Problem/Motivation
When you edit a field block on Layout Builder, modify the Title, check Display title, and save the block the field block does not display the specified Title (configuration label) but instead displays the label / admin label.
This is due to the block.html.twig template currently using the label variable.
Proposed resolution
Although this could be handled via a template override or a field block specific template (e.g. block--field-block.html.twig), this could be more cleanly handled by using a hook_preprocess_block that would replace the label with the configuration label, when available.