Do you mean just download it from itch.io, or is there something else?
Well, I downloaded Mindustry straight from itch.io and I'm still in release build 123.1.
Edit: I have an Idea for a way to update it and still keep all of my save data, and it's pretty simple; I just export my save data, re-download Mindustry, and import my save data. Would this work or is it stupid?
Idk but I'm gonna try it
Edit: Ok I'm not sure what happened, but this is what I did: I exported my data. downloaded another copy of Mindustry, tried to import the data, got a couple errors, checked Campaign, and somehow I have all of my data in the new copy. not sure if it was me trying to put the data in that made it work, or if Mindustry keeps data across multiple copies. But regardless, it worked!