I need help with FightCade on Windows 10

i moved over to windows 10 for about a month now and I really enjoy it, but the one thing that bugs me is that every time I try to use fullscreen while playing online I get a slow down in game. I think this is happening because of desktop manger or the fact win 10 uses directx 12 but I’m not for sure. If someone could help me that would me much appreciated.