external monitor gets only 50Hz

That site is in Spanish. When I run it through Google Translate, instead of getting an English translation of the page, I get an English translation of a message from the site telling me I tried to load a page too quickly.

What I could pick up:

• It is an Xiaomi G34 monitor
• It is a 34" monitor with a resolution of 3440 x 1440 pixels
• It has two DisplayPort inputs and two HDMI inputs
• It has a (maximum) refresh rate of 180 Hz

Given that the M2 MacBook Air has native DisplayPort output on its USB-C ports, a USB-C to DisplayPort adapter would have involved slightly less signal conversion than a USB-C to HDMI one. I don't think you would get 180 Hz or anything close to it even with a USB-C to DisplayPort adapter, given your Mac's Technical Specifications.

I believe that MacBook Pros with M2 Pro and M2 Max processors are capable of driving a 4K display over HDMI at a refresh rate of up to 240 Hz, at the cost of not being able to drive as many external displays, total. But those are more capable processors. Your MacBook Air has a plain M2 chip and I have never heard of any plain M-series chip supporting a refresh rate that high.

EDIT: Even on a MacBook Pro whose HDMI port could drive a monitor at 240 Hz, you would be limited to 100 Hz or less by the monitor (see below).

Elsewhere, I found this description of the monitor.

XIaOMI – XIaOMI Curved Gaming Monitor G34WQi

The DisplayPort ports are v1.4 ones and the HDMI ports are v2.0 ones.

On a site that had a copy of the "Xiaomi G34WQi Instruction Manual", I skimmed the manual, and saw

• "DP Maximum Refresh Rate: 180 Hz"
• "HDMI Maximum Refresh Rate: 100 Hz"

but nothing more detailed than that. (Dell's site often has long user manuals with tables that show all of the preset resolution / refresh rate / input combinations a particular monitor is designed to accept.)

A table that I found here

https://www.displayninja.com/which-cable-do-i-need-for-144hz/

suggests that for monitors with 3440x1440 resolution that have HDMI v2.0 ports, 100 Hz is typically the maximum refresh rate those monitors support on their HDMI inputs.

You could try a USB-C to DisplayPort adapter cable, and see if that got the refresh rate to go up from 50 Hz to 60 Hz. I'm not making any guarantees, but it might.

What model of monitor and what adapter and cable are you using to connect it to the Mac? Note that the M2 MacBook Air can support one external display with up to 6K resolution at 60Hz. To my knowledge it won't support a refresh rate higher than that.

MacBook Air (M2, 2022) - Technical Specifications - Apple Support

MacBook Air (15-inch, M2, 2023) - Technical Specifications - Apple Support

For a M2 MacBook Air that has either size of screen: "Simultaneously supports full native resolution on the built-in display at 1 billion colors and one external display with up to 6K resolution at 60Hz"

Hi,

Following thread could help your question.

External monitor refresh rate - Apple Community