M4 MacBook Air DP alt mode not working

[MLM]

I just got the M4 MacBook Air.

Previously I would hook up an M3 Pro MacBook Pro to my Asus PG32UCDM monitor through DisplayPort Alt mode and get power, display and USB through the single cable.

But with the M4 MacBook Air this is not working. I get no USB, and the display signal is crippled to 100Hz HDR.

 

[DaniTheFox]

This is indeed a significant issue. With the introduction of the MacBook Air M1, they introduced Thunderbolt 3 (TB3). Initially, there was a misconception that TB3 Must offered two DisplayPort (DP) streams. However, the TB3 specifications only required one. Previously, all MacBooks had Intel chips with two DP streams.

Currently, the M4 MacBook features two DP streams, whereas the M1, M2, and M3 models only have one. The implementation of DP streams can vary, and some monitors may not support them properly. The DP implementation in monitors is indeed complex.

 

[Vfqr]

Could you give some more details?
Are Apple M4-based computers experiencing a problem when connecting an external monitor via USB-C?

I want to upgrade my Air M1 to Air M4, and also I have a Dell U2723QE monitor that I connect to Macbook via a single USB-C cable. Can I somehow figure out whether such a setup will work before buying a new notebook?

UPD: tested with Macbook Pro M4 Pro (not Air) - all 3 ports works good (video + power delivery + usb hub)