Microsoft did not intend for OneDrive to be mapped as a network drive, and they don’t recommend the practice. Instead, Microsoft envisioned OneDrive as integrated into your computer’s File Explorer (hence the name “OneDrive”), and designed its Office 365 services and features around that vision.
The intended usage is to sync SharePoint files with the OneDrive sync client, which provides Files On-Demand, allowing you to access all your files in OneDrive without using local storage space. You can even access the files when you're offline.
While it is technically possible to associate OneDrive with a drive letter on your PC, doing so employs older technologies and introduces a raft of potential issues. Among those:
- Mapping a library as a network drive is temporary and supported only through Internet Explorer
- You have to occasionally visit the site on your browser to make sure your login doesn't expire, on every machine you want the mapping to persist
- File operations are very slow
- You may experience unexpected behavior
- Sharing from the context menu does not work
See this Microsoft support document on how to set up syncing using the OneDrive client.
This Microsoft support article has information on troubleshooting mapped network drives that connect to SharePoint Online.