Thanks for reporting. The issue is due to an unused Python package (dicom2nifti) released a corrupted version for Python-3.9 a few days ago. The error is reported to dicom2nifti developers and a fix is already implemented in TotalSegmentator extension.
The fix will be available in the Extensions Manager from tomorrow. If you use the latest Slicer Preview Release (currently Slicer-5.8.1), then tomorrow you can go to the Extensions Manager and click “Check for updates” and then “Update all” to get the fix.