UK John, you did mention that you BOUGHT the game :
I bought this game, and interestingly, I can download the update here for free, but this update is NOT on my download page!
What NiiChan is saying is you can download for the game for free, but if you support the project via Patreon, you will get early updates.
There are many games on Itch that use the same model for downloading for free or support the developers via Patreon and get the updates first..