Unable to select the maximum available display for my Lenovo P24q-20 monitor

Hi, I'm having a problem on my macbook air early 2015, where in the systems preferences > display, I see the list of resolutions that I can select for my external monitor (Lenovo P24q-20) but it does not have available its max resolution of 2560x1440. I have tried the method of pressing Option whilst I select to radio button to change the resolution, this does bring up many other resolution options, but still the desired resolution of 2560x1440 does not show up. The highest resolution showing is 1080p.

Here is the specs for the monitor, it looks like it should display that resolution: https://support.lenovo.com/us/en/solutions/pd500388-thinkvision-p24q-20-monitor-overview

I'm using a hdmi cable, with a hdmi to mini Display port adapter to connect to the macbook air.

Any ideas on what I need to do to resolve this problem?