The critical part of Dropbox is not just the storage layer but a combination of their client and server. Even small things like how do you handle conflicting writes to the same file from multiple threads, matter a great deal for data consistency and durability.
A lot of the backend bucket providers can handle file versioning.
I too would like the answer to this concern because the features page doesn’t mention it. I want to be able to handle file version history.
I’m currently using Filen which I find very reasonable and, critically, it has a Linux client. But I wish it was faster and I wish the local file explorer integration was more like Dropbox where it is seamless to the OS rather than the current setup where you mount a network share.