There is no way to trigger the upload dialogue without a mouse click or touch. There should be a keyboard-based method to trigger this upload.
There appears to be two ways to address this:
- Classic Sakai: Sakai 10 offered the "Switch to file browser upload?" option, revealing the <input type="file" /> option. Restoring this functionality, perhaps in a means that is only made visible as it is tabbed to, would allow keyboard navigation users to select with their keyboard and launch the browser's file picker.
- Add a button element: As described in this dialogue https://stackoverflow.com/questions/39999425/dropzone-js-accessibility adding a button element can provide a tab'able element.
- In Resources tool choose Add > Upload Files
- Using your keyboard, hit the Tab key to try to navigate to the upload dropzone.
- Clicker enter within the dropzone should open the browser's file picker, if you tab beyond to "Overwrite existing files" the dropzone is not keyboard accessible