Spamming the forums won’t help. I’ve never seen a DX12 game use Exclusive Fullscreen. It always causes problems. When WoW made the switch they abandoned Exclusive Fullscreen because they couldn’t get it to work in DX12. It may have been labeled incorrectly. Also, here’s some info. I hope your situation fixes itself broski. I doubt they will let the resolution problem last all weekend.
Exclusive Fullscreen Instability in Beta - Technical Support - Diablo IV Forums (blizzard.com)