Well hells bells!!! I just used dgVoodoo and it fixed the problem! I guess it helps pass-through the EMU's old dx version and utilizes current features. Now I can full screen with no issues!
It's actually pretty simple! I did try to see if it would do 4k when selected in KF's resolution. But it maxes out at 1080p regardless.
Also, this wrapper from what I am reading should work on any older DX or 3dFX or Glide software. So this may fix older emu, Windows games and much more!
5thWolf's post in Kega Fusion + highdpiaware was marked as the answer