MacBook Air not extending image on 2 external displays

As far as I can tell you're going to need 2 USB-C to HDMI adapters...

Amazon.com: USB C to HDMI Adapter 4K for Mac OS, Type-C to HDMI Adapter [Thunderbolt 3], Compatible with MacBook Pro 2019/2018/2017, MacBook Air, Galaxy, Dell XPS, Pixelbook, Microsoft and More (1 Pack) : Electronics

More on the adapter you have...

Windows OS supports both SST and MST mode

Amazon.com: USB C to Dual HDMI Adapter 4K @60hz,Type C to HDMI Converter for MacBook/MacBook Pro 2020/2019/2018,MacBook Air,Chromebook Pixel,LenovoYoga 920/Thinkpad T480,Dell XPS 13/15,Surface Book 2, etc : Electronics

Why can't I use two displays on a Mac computer?

The reason has to do with the technologies for display used in macOS computers vs Windows computers. Mac utilizes Single Stream Transport (SST), while Windows allows for Multi-Stream Transport (MST) on most devices:

• What are SST and MST? In order to achieve 4K resolution at 60Hz, most early 4K displays on the market used Multi-Stream Transport (MST), a technology that stitches two halves of a display together into one large surface -- also called a "tile" -- in software. MST, supported on Thunderbolt 2 Macs, can carry a signal for two or more monitors on a single cable, allowing for daisy-chaining or hub configurations of multiple 4K monitors. 
• 
  
• More recent 4K displays have started using Single-Stream Transport (SST), eliminating the need for stitching two halves of a display together in software. Instead, SST monitors feature scalers that support 4K resolution at 60 Hz over a single tile. Ideally, if you are purchasing a 4K display, you should look for one that supports SST, since MST can cause issues with in-game menus, BIOS screens, and scaling.

On Mac OS with Intel's processor lineup, it supports DisplayPort 1.3. Macs with DisplayPort 1.3, will be able to drive a 5K display over SST, eliminating the need for Apple to worry about syncing two channels over MST.

Does my device support Multiple Monitors? – HYPERSupport (zendesk.com)

Hmmm,

• It supports mirror or extend mode for Mac and extend mode, showing the same image on both extended monitors.

Comsol USB-C to Dual HDMI 4K Adapter | Officeworks

First review there...

Tim M

Melbourne, Australia

• Review 1
• Votes 71

☆☆☆☆☆

☆☆☆☆☆

2 out of 5 stars.

· a year ago 

Warning: does not support 2 separate displays

This works, BUT - not how I expected it to. I was intending to connect two separate displays, but instead it only allows one separate display, duplicated on to two monitors. It's essentially a double adapter, not a double display device. This isn't clear in the product description.

Is it just one adapter? A splitter? If so you need a separate port & adapter for each monitor.

Which year MBA is it?

Video Support

Simultaneously supports full native resolution on the built-in display at millions of colors and:

• One external display with 5120-by-2880 resolution at up to 60Hz
• Up to two external displays with 4096-by-2304 resolution at up to 60Hz

https://support.apple.com/kb/SP798?viewlocale=en_CA&locale=en_CA