I researched a lot about this topic - but I still haven’t found a working set.
A repeater/loop/add more/infinite field, which allows to add multiple items of arbitrary amount to a post (in admin backend).
Each of these items in repeater/loop list should contain a simple text field and a relationship/post selection field with which a post (ideally filtered by type) can be selected.
Finally it should be possible to pre-populate such a repeater/loop list programmatically (using PHP code, in a plugin) in a specific post type admin backend page.
It appears that WordPress plugins or frameworks/libraries only partially implement one of these needed features - but never everything - and loop items cannot be extended by other plugins, they are usually an internally used data structure.
Are there no free or opensource plugins or frameworks that offer this functionality?
What existing code can be build on to add this functionality by reusing as much as possible?