Why can't I get a 144hz on 1279x1080?

Moin first together,

If I play Fortnite on 1280x1080 I can enable 144hz, but if I play at 1279x1080 can't I?

If who knows why this could be or how to fix it, thank you in advance schonmal

The resolution does not exist. You can't just magic away the one pixel.

But that is there, that you can see the crosshair better and use this Res eig quite a lot, so I'm surprised.