Files in the version history of OneDrive can also take up the available space. These can be deleted by following the steps below.

Locate the file(s) you wish to delete the Version history of, and click the three double dots and select version history (as shown below)

Once in the version history, click the three dots against the oldest version(s) of the file and select Delete Version, as shown below.

This will then move the deleted version to the Recycle Bin.