According to this Microsoft support document: support.office.com/.../Manage-large-lists-and-libraries-in-Office-365-b4038448-ec0e-49b7-b853-679d3d8fb784
"OneDrive for Business is a personal library intended for storing and organizing work files in Office 365. Using the OneDrive for Business sync app, you can also work with files on your local computer and synchronize changes between your local computer and Office 365. Unlike document libraries in a team site, the OneDrive for Business library has a List View Threshold of 20,000 items."
Then the support document support.office.com/.../Move-SharePoint-Server-2013-OneDrive-for-Business-files-to-Office-365-64b845b2-e5e9-4736-b7f1-a2ed2bae012b then goes on to state:
"The sync app can sync libraries containing up to 20,000 items."
"If your OneDrive for Business library has more than 20,000 items, you can’t use the sync app as described in this article to move your files to Office 365. The item count in OneDrive for Business is comprised of files and folders in the library, plus any files in your SharePoint recycle bin."
"If possible, reduce the number of items you’re storing in OneDrive for Business so that you can use the sync app to move your files as described in this article.
If you really need to move more than 20,000 items, you can use the Open with Explorer option, though it may take a long time to do this. For details, see Video: Copy or move library files by using Open with Explorer. Alternatively, a programmer may be able to create a script to move your files more quickly."
So they Microsoft appear to be claiming a List View Threshold of 20,000 items and that it is possible to add more than 20,000 items to your Office 365 OneDrive for Business.