@lambuzz 

Hi,

Regarding your first point. Have you seen information on the product itself or on TP-Link's website that points to the Archer AX55 V1 supporting MU-MIMO?

Regarding your second point. What year was your MacBook Air manufactured? The Wi-Fi capabilities depend a lot on the age of a wireless device.
 

Hi,

MU-MIMO was listed on the amazon page. 

I also found another community page about this feature on the AX55 and it seems to be supported

https://community.tp-link.com/en/home/forum/topic/539526

I have a 2022 M2 MacBook Air and it fully supports Wifi 6. 

  @lambuzz 

Ok, so the thread you've linked to pretty much clears up the matter of MU-MIMO on the AX55.

But no matter what the state of MU-MIMO on the Archer AX55 is, a 2022 MacBook should be able to get 500 Mbps over Wi-Fi.

How far is the MacBook Air away from the AX55? For speed testing you should be close to the router.

What is the "Link Speed" or "Tx/Rx Rate" of the MacBook Air as shown by the AX55 or, if available, by the MacBook?

Have you activated QoS on the AX55? If yes, then switch it off.
 

  @woozle 

I am sitting next to my router.

The Link Speed is 960mbps with the Macbook 

QoS is disabled 

The weird thing is that I can reach a max upload limit of 534 mbps but it's the download that doesn't seem to work properly

  @lambuzz 

Do you own any other devices you can use to crosscheck these results?

And try a second speedtest platform (e.g. speedtest*net, fast*com), also as a crosscheck. 

If the results are consistent, then try whether setting the AX55 to another 5 GHz channel that falls into another band makes any difference.
 

  @woozle 

I tried with another laptop (XPS 13) and a Pixel 7. Similar results. For the XPS, I even have full speed when connected to ethernet

I tried with several speedtest platforms for similar results.

I tried different 5Ghz channels. I also selected the one with the least wifi from the neighours.