Why does the monitor not display 4k resolution when connected to a macbook?

Question

LG

Good evening! The crux of the matter is this.
I have an old macbook air, early 2015.
However, the specifications indicate that it can connect a 4k monitor:
Dual screen and video duplication modes: simultaneous support for full native resolution on the built-in screen and up to 3840x2160 pixels on an external monitor; high color quality in both cases (millions of colors)

And there is a new LG 27UL650 monitor that supports 4k. I connect with an adapter miniDisplayPort-HDMI, Cablexpert A-mDPM-HDMIF-02, 20M/19F + native hdmi cable.
The problem is that when I connect a macbook to the monitor - the monitor gives out a maximum of 1080p and the picture is all smeared.
In resolution offers, it only outputs 720p, 1080p, and 1440x900.

What could be the problem? Thanks in advance.

Answer 1

Use Thunderbolt - mini Display port