Want to connect Dual Monitors to my MacBook Air M3

You can use 1 external monitor and the built in screen of the MacBook Air, or you can use 2 External Displays, but without using the built in screen by closing the MacBook Air's lid. You cannot use 2 external displays and the built in screen at the same time.

To get them to extend instead of mirror, you would need to go into System Settings ➜ Displays, click on the picture of the display you can to extend to, and then in the Use As dropdown click on "Stop Mirroring".

click here ➜ Extend or mirror your Mac desktop across multiple displays - Apple Support

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

Extend or mirror your Mac desktop across multiple displays - Apple Support

Note that

• Your Mac only supports using external displays when its lid is closed.
• Macs in general do not support DisplayPort MST daisy-chaining, and do not support attaching two displays to a plain (non-Thunderbolt) dock or hub.