Попробуйте:
# ...
def launchHud(self):
window_handle = user32.FindWindowW(0,WINDOW_NAME)
if window_handle != 0 :
self.hud = Hud(window_handle)
self.hud.setWindowFlags(self.windowFlags() | # <---
Qt.FramelessWindowHint | # <---
Qt.WindowStaysOnTopHint) # <---
self.hud.show() # <--- !!!
# ...