Oh, interesting – I wasn’t understanding that either initially. One option would be to use the Tab key to get down to the publish button. Essentially keep hitting tab key like 14 times until right after “limit scaling to” field, and then you will be on the ‘ok’ button, and hit Enter.
Perhaps you could also adjust your Taskbar Settings temporarily to “Automatically hide the taskbar in desktop mode”, and see if the OK button is visible then? (right-click on the taskbar, Taskbar settings, then find the option listed above).