webp support was dropped in d1f2e

I can confirm downgrading to 3.1.0 fixes this issue for us.

We had the same issue with WebP module and Stage File Proxy. After rolling back to 3.1.0 the issue is gone.

Same case. 3.1.0 is the last working version.

MRs are welcome

I think the image download controller has to similar things. \Drupal\image\Controller\ImageStyleDownloadController::deliver uses \Drupal\image\Controller\ImageStyleDownloadController::getUriWithoutConvertedExtension