This bit of documentation was unfortunately not accurate, it came up a little while ago from another user. Dorico won’t leave a partial final bar this way. I’m sorry for the confusion! I always check everything I write, so that was either briefly true but is no longer or I was simply mistaken.
It’s been corrected in-house since the 3.5 manual was published, as you can see here in the iPad manual. Again, apologies for the misdirection - adding an explicit barline and removing the final bar after the barline, or adding a time signature with fewer beats for the last bar are both available alternatives.