Help with kvm. Says out of range.

I have finally bought a KVM, but it says "out of range". My resolution is set to 2560x1440, which is 4K. The monitor is an MSI MAG322CQR, which I have been using with the PCs for a few years.

All the PCs work when I put them into the monitor HDMI ports, but one fails with the KVM. My Dell running Mint at the same resolution works fine through the KVM, my NVR and Raspberry Pi (I don't know what resolution) work, but my OpenSUSE machine says "out of range".

A friend let me borrow his KVM and it does the same thing. Both are 4K KVMs. What am I doing wrong? Thanks in advance.