Hi Carles, I wanted to let you know I fixed the secondary screen issue in version 1.2.2 and it's available on the Itch App and the Pixel Fireplace Downloads Page. Let me know if it fixed the bug you were having.
Hi Ted, thanks for letting me know! Sorry to be a downer but unfortunately it seems it's still not working correctly for me :(. I've removed the previous version and installed the latest one you have uploaded (tried via the Itch app and also via the downloads page). After starting it, double clicking to switch to windowed mode, dragging the window to the second monitor and double clicking there again, it switches to fullscreen mode but back on the main monitor. It doesn't want to stay in the second one.
Okay, that's what I'm on too. Would you mind trying out a debug version? It'll show the variables used for the displays and game-window xy positions, and sizes. You can email me at tedmartens [at] gmail [dot] com
Also, before going fullscreen pixel fireplace checks the top-left corner of it's window to determine which display to go to, so if the window isn't all the way within a secondary display it will go to the main display or whichever display that corner is within. It defaults to the main display if the top-left corner is outside of all display borders as well. Make sure you've dragged the window all the way to your secondary screen before trying fullscreen. (I might change it so that it checks the center of the window instead of the top-left corner)