Yes I've tried one that is working with 4k and 60hz on my TV.Are you using a HDMI 2.0 (Ultra High Speed I think? I hate HDMI's cable branding...) cable? if you're using an older 1.4 cable there isn't enough bandwidth for that resolution at 60Hz.
Thank you, thats the next step I'll try nowMaybe try uninstalling and re-installing display drivers.
Yes I found that too but I wonder why I can Display a higher resolution in 60hz (as you can see on the screenshot i postet)From what I found online the 750Ti has HDMI 1.4 and therefore only supports 4K 30Hz.
Yes I found that too but I wonder why I can Display a higher resolution in 60hz (as you can see on the screenshot i postet)