After discussing with Pierre, indeed not a bug, but rather an UX / Label issue that might lead to confusion.
Proposed resolution
Introduce categories/group in the select output when selecting data from a field to further explain the context.
To take it further
When already in a field context, remove the same field from the select options of Data from a field to avoid context loop/duplicate or display warning upon selection.
hproustacx → created an issue.
First issue :
in web/themes/contrib/ui_suite_dsfr/components/share/share.twig Line 6 should be
{% set link_attributes = link.link_attributes|default({}) %}
to allow attribute from menu or other entities
Second issue :
There is no way to properly contribue that component in Drupal, you either have to do some custom entities, or rework the links in Javascript
Possible solution would be to contribute that component as a menu and use token in the url field to respect the pattern of the DSFR example :
https://www.facebook.com/sharer.php?u=[ insert current page url]
hproustacx → created an issue.
pdureau → credited hproustacx → .