Hi Lowri,
People have reported success with the following solution - kindly let me know if it works.
• Press Windows + R to open the Run dialog.
• Type services.msc and press Enter.
• Locate Microsoft Account Sign-in Assistant in the list, right-click it, and select Restart.
• Locate Microsoft Cloud Identity Service, right-click it, and select Restart.
• Reopen Onedrive and try signing in again.
I’m eager to hear back and work together to find a solution.