@Danny12345678912 I had the same problem.
HP Elitebook 840 G4 -> 2560x1440 as a maximum resolution in Windows when HDMI is used from laptop.
The problem is that HP Elitebook 840 G4 has HDMI 1.4 which has bandwidth not enough even to do 3440x1440 with 60 Hz.
Quick and dirty fix for Windows -> create custom resolution 3440x1440 56 Hz ( this tool is nice for Windows https://www.monitortests.com/forum/Thread-Custom-Resolution-Utility-CRU )
Going to buy Thunderbolt (USB-C) -> DisplayPort cable and and try it out, it supposed to have 20 Gbit/s throughput.
And yeah, regarding 4k you have been able to do before - it was definitely not 4:4:4 60 Hz.
https://pasteboard.co/Jqh7whh.png
Bought the monitor via Amazon.de (it was the cheapest option for Sweden). 1 dead pixel and 2-3 subtle dark spots (not sharp as dead pixel, might be some dust or whatever). Overall, satisfied with it.
HP Elitebook 840 G4 -> 2560x1440 as a maximum resolution in Windows when HDMI is used from laptop.
The problem is that HP Elitebook 840 G4 has HDMI 1.4 which has bandwidth not enough even to do 3440x1440 with 60 Hz.
Quick and dirty fix for Windows -> create custom resolution 3440x1440 56 Hz ( this tool is nice for Windows https://www.monitortests.com/forum/Thread-Custom-Resolution-Utility-CRU )
Going to buy Thunderbolt (USB-C) -> DisplayPort cable and and try it out, it supposed to have 20 Gbit/s throughput.
And yeah, regarding 4k you have been able to do before - it was definitely not 4:4:4 60 Hz.
https://pasteboard.co/Jqh7whh.png
Bought the monitor via Amazon.de (it was the cheapest option for Sweden). 1 dead pixel and 2-3 subtle dark spots (not sharp as dead pixel, might be some dust or whatever). Overall, satisfied with it.