The Wikipedia entry for learning objects starts with the current definition from the standard: "any entity, digital or non-digital, that may be used for learning, education or training". That is a vote of confidence in the standard, which is heartening, but doesn't help improve it. Other definitions given tend to be longer and more technology specific.
Also I did a quick literature search. A paper which featured prominently was Sosteric and Hesemeier (2002) in IRRODL (my favorite educational journal, as it provides HTML as well as PDF versions. They also start with the IEEE, asserting '... a definition that includes “everything” is not a definition at all ...'. They also question if "digital" is useful. In my view qualifying leanring with "digital" is little more than window dressing.
Sosteric and Hesemeier (2002) describe as "counterproductive" the use of terminology from computing science. This is my own field, and it can be annoying when a computing term is taken and used, not quite correctly, in other disciplines. However, the authors have a more fundamental objection to learning objects, as it implies that learning can be chopped up into reusable, interchangeable "chunks". However, I suggest, to some extent, this is what learning designers and educational systems, do. An extreme example is the Australian vocational education system, where 1,300 qualifications are made up from 16,000 of "Units of competency", all listed in a database.
Sosteric, M., & Hesemeier, S. (2002). When is a Learning Object not an Object: A first step towards a theory of learning objects. The International Review of Research in Open and Distributed Learning, 3(2). https://doi.org/10.19173/irrodl.v3i2.106