This commit might help:
https://github.com/kovidgoyal/calibr...33eeb9657526cc
Or you can just get the window back on screen with this
https://www.tenforums.com/tutorials/...dows-10-a.html
and hopefully it will stay on screen after doing that once. Or you can delete the main_window_geometry key from gui.py.json in the calibre config directory.