"Could not create the work file” error in Office

Symptoms

When you try to preview or save a document, Word returns the following error message:

Word could not create the work file. Check the temp environment variable.

https://learn.microsoft.com/en-us/office/troubleshoot/office-suite-issues/no-file-previews-file-explorer-switching-to-32-bit

I fixed it by deleting the registry key for Word