What is a digital platform?
I am not aware of any definition, and believe me, lots of people would like to have one - mostly for regulatory purposes. There are attempts in many countries to regulate digital platforms, but without good definition, you can't create a good legal regulation.

Any definition I have seen so far is a list of features, that is, however, not exhaustive - it would be a good definition if we could say, "it is a platform if it has those 8 features," but then you will find one that doesn't have all of them, and you find something that has all of them, but you won't call it a platform...