Special:Upload is mostly usable on mobile, but there are a couple things that should be improved:

• The desktop version has some Javascript that runs once the file is selected. This Javascript:
  1. fills in the 'destination filename' field
  2. generates a thumbnail of the image
  3. applies rotation to this thumbnail if required
  4. checks to see if the file already exists on the wiki
  5. checks if the file is larger than the allowed upload size
  6. previews the chose license
  7. warns of leaving the page without submitting the made changes

This Javascript doesn't run in the mobile version, probably because it doesn't have target=mobile.

• Add the ability to have a link for it in the main menu based on a feature flag (similar to the old Special:Uploads link, with same icon).