Macbook Air M3 only detecting one out of two monitors through dock

Your M3 MacBook Air supports one external display with the lid open; two with the lid closed.

Use dual monitors with your MacBook Air and MacBook Pro with M3 chip - Apple Support

To connect two monitors to the same Mac host port In a supported way, that port must be a Thunderbolt port – and the device connected to it must be a Thunderbolt device (dock, hub, or dual-display adapter). Thunderbolt offers a wider "data highway" than plain USB-C (DisplayPort Alt Mode), and Macs want to see that wider "highway".

The HP USB-C Dock G5 that you mention does not appear to be a Thunderbolt dock.

saaimac wrote:

Thank you very much for the prompt reply. As per HP's website, I was under the impression that the HP Dock G5 is a thunderbolt dock.

HP USB-C Dock G5

"Designed with universal compatibility in mind, this dock works with both HP and non-HP USB-C®- and Thunderbolt™-enabled laptops. [1]"

"[1] For USB-C® functionality, host PC must support the DisplayPort™ Alt mode protocol through its USB-C® port. Thunderbolt™-enabled notebooks will function at USB-C® speeds."

and the "minimum system requirements" are "USB Type-C®️ (USB Power Delivery, Alt Mode DisplayPort™)".

I could be mistaken, and this could be a device that works with either Thunderbolt or DisplayPort Alt Mode, but my instinct says that it is one that always works with the latter. HP is mentioning Thunderbolt to reassure people that have computers with USB-C ports that support both Thunderbolt and DisplayPort Alt Mode that the dock will work with them.

On a side note, does this seem to be a dock that would solve my problem? Here's a link to the dock: Amazon

The vendor tells you that it won't work. From the About this item text:

"For OS system, it is also a mac mini dock, but please note it only supports mirror mode and non-mirror mode. Non-mirror mode means that the three external monitors are the same but different from the laptop. Please note: When two or more monitors are connected, each monitor will be limited to a maximum resolution of 1920 x 1080@60Hz."

On the "Mac OS-Triple Display" slide: "Please be advised that MST (Multi-Stream Transport) is not supported by macOS, resulting in identical images displayed on external monitors."

Despite the "Thunderbolt compatible" wording, this is not a Thunderbolt dock. They're mentioning Thunderbolt to reassure you that the dock will work as a USB-C (USB, DisplayPort Alt Mode) dock if you plug it into a Thunderbolt 3 or Thunderbolt 4 host port on a computer. That doesn't mean that the dock understands or can take advantage of Thunderbolt.