The difference is that the remake has a different build. So the UI is different and so is the mechanics. It's got some quality of life improvements from the itcho version, but play similarly.
It is mostly the same game though. Nothing has been really redesigned enough to call it a new game compared to an update. It's still 95% the same art assets. It's slightly more simplified than the itch.io version mechanically aswell (Which is fine).
Personally I prefer the itch.io version. The steam version has a lot of things removed that I personally liked about the itch.io version. Minus the custom gamemode it hasn't really "added" anymore to the game. The quality of life stuff is nice though.