A Microsoft file hosting and synchronization service.
To be honest, I haven't tested it extensively - this was more an inconvenience and a principle issue for me. I mainly just went to the iOS Files app and went to move a file from there and verified that when I selected OneDrive as a destination the Move button was again blue on not grey.
Please do elaborate when you have time, I have a little time at present to play around with things and nag these gods.