0.18 is no longer part of the public build phase. In this phase, saves can be transferred from 0.19 to 0.21. Development-wise, I can't predict how the game will look in a year, so I can't promise saves can work between versions that old. So 0.18 might or might not work. I have no idea how steamdeck works, so you'll have to google that. The engine the game runs on is RPG maker MV.