Impossible to change resolution to highest on MacBook with monitor

Hello,

I have a MacBook Pro mid-2012 13", under macOS Catalina 10.15.7. I bought a MiniDisplayPort to HDMI adapter (it works in 4K 60hz, as my HDMI cable does, and it's the version 1.2 of DP) in order to connect my Mac to my monitor (my monitor is a LG UltraWide 29BN650-B 29" with a resolution of 2560x1080 pixels).

The problem is that I can't define the resolution of the display on 2560x1080 pixels when I go to my Mac's settings. I even tried to change the resolution in the monitors settings by pressing the option key (alt) : the maximum resolution proposed is 1600x900. So i let the settings on "optimised for LG HDR WFHD" and not on "scaled", but it does not fill the whole monitor display unless I change the picture format of the monitor for "full Wide" instead of "original", but it expands the icons so that's not what I want. I thought the problem was coming from my MacBook which may not support the resolution, but after doing some searches it can support up to 2560x1600 pixels of resolution.

If anyone knows how to solve this problem and define the resolution to 2560x1080, it would help me a lot, thanks :)

PS : I also tried to change the settings of the DP version on my monitor to 1.2 instead of 1.4 but it didn't change anything, and I think the problem may come from the fact that the cable is a Mini DisplayPort instead of Thunderbolt but idk if it changes something.