Hello @Martin Härri
Dionathan with ALM Works here.
You could use the following sample formula and let me know how it goes (PS: this formula will work only on the latest versions of Structure (V7.0 +)):
issueLinks.FILTER($.type.outward = "is parent of" AND $.destination = this).MAP($.source.key CONCAT ' - ' CONCAT $.source.summary)
issueLinks.FILTER($.type.inward = "is parent of" AND $.destination = this).MAP($.source.key CONCAT ' - ' CONCAT $.source.summary)
depending on your setup.
Basically, it is filtering the issue links by "Is parent of" and it should show the Issue Key + Summary in a Formula Column.
Please refer to this article for more information about Item Property Reference
If any further questions, let me know.
Customization in Board is not possible as of now in Jira Work Management Template Projects.
If you need configurations you can choose to create a kanban board where you will have more control over how cards can be displayed.