4k - LoL Won't Full Screen @ 3840x2160

When you use fullscreen you set the resolution. I don't think 3840x2160 is offered. Just use borderless, it achieves the fullscreen look but without causing potential issues alt-tabbing and such...

ok found a riot post on the window bug:

So there's a kinda ugly bug where the bottom option in each option drop down is still there, but not initially visible. If you scroll down, it's still there. I've let the team know, thank you for the heads up!