says
HDMI (v2.0)x2
DisplayPort (v1.2) x1
MiniDisplayPort (ver1.2)x1
HDCP 2.2
what hdmi cable are you using ? does the iGPU in your Librem laptop and the driver support hdmi 2.0 and hdcp 2.2 ?
if the monitor/cable/igpu/driver all support 4k@60hz it should work on first try - or even 4k@30hz