After three days of research on the subject, Adam Engst of TidBITS has provided a detailed explanation of what’s happening with cloud-storage providers on macOS Ventura:
My understanding is that Box, Google, and Microsoft have migrated their Mac users to the File Provider approach, whereas Dropbox—probably the most popular among everyday Mac users—has only recently started to encourage those outside its beta program to switch (while others are still being asked to join the beta).
Adam’s story has all the details. In short, Apple is having all these apps migrate away from kernel extensions and to an Apple-built API, leading to some major changes in how they work and how users interact with them.
—Linked by Jason Snell