Responsive images are not being generated

[ogradye]

$car->addMediaFromDisk('/cars/tmp/' . $fileName, 'spaces')->withResponsiveImages()->toMediaCollection('cars');

No responsive images are generated. When I called withResponsiveImages the following happens:

• the information is added to the media table with the responsive array empty.
• The file is placed in storage/media-library/temp (I find this odd, and wouldn't like this to happen as the files should be stored on a remote object storage service)

No exceptions are thrown.

[Don404]

Is the image "webp" format?