A Microsoft file hosting and synchronization service.
I am having the same issue on my Mac OneDrive - shared folders are not showing in my Finder window on my computer or on my OneDrive online. My business OneDrive shared folders are not showing on my personal OneDrive.
The shared folders are also not showing up when my business OneDrive folder is shared with another licensed user within my business. They can see the shared folder in their online shared section, but not on their computer OneDrive folder.