I actually didn't know that you can do that. I add Steam keys to the itch.io purchase now. This is the first time I have done this so let me know it works or not :)
Viewing post in Fate and Life: The Mystery of Vaulinhorn Deluxe Edition comments
I have now bought it via Itch. I received the Steam key after the purchase and was able to activate it without any problems. Thank you very much that it works with the Steam key.
Edit.
It also runs on the Steam Deck. For the controls, you have to set the layout with WASD(mouse) and can then control the mouse with the trackpad.