Adding multiple external monitors to MacBook Air M3 running Sonoma 14.6.1

How are you connecting these monitors? You can only connect two monitors to one Mac host port if the device that is plugged into the Mac is a Thunderbolt device, like a Thunderbolt dock.

Macs don't support DisplayPort MST daisy-chaining, and any "plain" USB-C hub or dock with two or more monitor outputs is likely to be using some second-class workaround method (that requires installation of special software) to support some or all of them.

sjcecran wrote:

I'm connecting using a Selore &5-Global USB C to Dual HDMI Adapter, similar to this one. It has two HDMI ports and five USB ports (3.1, 2.0) and the output is USB C.

The online manual for that one has a section whose title is "Extended Desktop (NOT supported by APPLE). I do not see any mention of having to install a special driver on your computer, so I am guessing that this device uses native USB-C (DisplayPort Alt Mode) output – but does the equivalent of DisplayPort MST daisy-chaining.

I'd gladly purchase a different hub/adapter/docking station.

Here are three vendors who carry a lot of Thunderbolt docks and hubs. The details of how you connect twin monitors varies from dock to dock. Some give you one dedicated video port, and let you connect a second display or adapter to a Thunderbolt daisy-chaining port. Others split a Thunderbolt chain into three or more chains, and let you connect displays or adapters to two of them.

Other World Computing

SonnetTech

CalDigit

There may be other Thunderbolt docks from brands like Belkin and Plugable.

You probably won't find a lot of Thunderbolt docks that have twin DisplayPort or twin HDMI interfaces - but as long as the dock has a HDMI interface and lets you plug in a USB-C to HDMI adapter; or gives you the ability to plug in two such adapters; you should be in business.