Drupal 10 issue
When uploading a custom WOFF font using FontYourFace module in /admin/appearance/font/local_font_config_entity/add, error appears. Seems to happen if you have File Entity module enabled:
Error message: The specified file .woff could not be uploaded. The referenced entity (file_type: undefined) does not exist.
Solution
Add the MIME Type in the File Type in /admin/structure/file-types/manage/
Create for instance Fonts File Type, then under the Mime Type add the following to support WOFF files, then save. In our experience, you simply need application/octet-stream, but the other types may be useful, too:
application/x-font application/octet-stream application/woff
After this, the uploading of the WOFF files should now work and you are now able to create your custom fonts using FontYourFace module.
