That's bizarre. That's the same version I have. The only thing I can think of is that your system language isn't English and maybe it removes that option. ¯_ (ツ) _/¯ If that is the case it's unfortunate that it doesn't work for different languages.
You could try switching the system language to verify that that is what is happening. I have no idea what kind of effort it takes to add that feature for other languages but you could always ask the Dev.
I like openboard because of the similarities to gboard and this fits the bill well. However I do agree that this fork doesn't seem active. But I have a feeling that perhaps it was just a personal project to add swipe to openboard.