The OneDrive is full notification can appear when
- you don't have enough space and you need to delete some files or increase the space.
- you have plenty of available storage, this error can be solved by unlinking your account.
If the app says that is not enough space to save your files, although there is plenty, just reinstall it.
To fix the OneDrive is out of space error, you can try to change the initial sync folder.
Try the following options:
Option 1 - Unlink your account
Right-click on the OneDrive icon in the notification area of the task bar and open Settings
Select the Account tab
Click on Unlink this PC button
Option 2 - Reset OneDrive
Press Windows Key + R to open the elevated Run command prompt.
In the Command Prompt window, type or paste in %localappdata%MicrosoftOneDrive.exe /reset
Right-click on the OneDrive icon in taskbar’s notification area and open Settings.
Sign in again.