Second external monitor on M1 iMac

The M1 iMac only supports one external monitor.

iMac (24-inch, M1, 2021) - Technical Specifications - Apple Support

"Simultaneously supports full native resolution on the built-in display at 1 billion colors and:

One external display with up to 6K resolution at 60Hz"

There are no products that can add more first-class hardware-supported display outputs.

There are workaround products using DIsplayLink and similar technologies that make it possible to attach two or more displays in a second-class way. These may involve compromises – such as lags, unsuitability for games or other rapidly-changing content, and having DRM-infested streaming services refuse to play video (even on your built-in screen) as long as any of the extra screens are hooked up.

OWC and SonnetTech both have DisplayLink-based dual monitor adapters.

There are also various USB-C hubs that have DisplayLink (or some other second-class workaround technology). Whenever you see a claim that a plain USB-C dock supports connecting more than one display, it will usually turn out that the device is relying on a workaround (DisplayLink, Magic Control Technology, etc.).

In the case of DisplayLink, Synaptics provides the "magic decoder ring" chip set that the adapter and hub vendors use. You must run DisplayLink software on your Mac in order to make use of DisplayLink-attached displays.

Synaptics – DisplayLink Graphics

DisplayLink Knowledge Base – Troubleshooting: macOS

Not likely as Apple says in the system specifications only 1 external display. However, contact Macsales.com and see if they have any adapters.