Hi Fixer! Many thanks for trying out the game on Linux. I'll try having an actual Linux build the next time I release a new demo. Out of curiosity, what version of Proton did you use on your Linux machine?
Happy to hear it works fine on your Steam Deck. I've used mine to try and optimize the game as much as possible on it, should run pretty well there!
I tried Proton 11, 9,5, and 10-GE. But the issue doesn't have anything to do with Proton. I realized a little later than all my games on PC weren't running well. Seems to be because I switch over to Wayland recently. When I changed back to x11 everything started running smoothly again including your game.
I made it to the boss fight but haven't beaten him yet. I found Project Goblin through r/Godot. I'm also working on a lowpoly action game (more soulslike than DD though) and its really motivational to see that one person can put together a great game like this.
If you do decide to make an native linux version and need someone to test it feel free to reach out.