As crooked-v noted, there is no native support within the M1 Macbooks for multiple external displays. Apple states this on the tech specs page in the Video Support section: https://www.apple.com/macbook-pro-13/specs/

You can workaround the issue with a Displaylink dock though. I've been using the Dell D6000 dock to run two displays on my M1 Macbook Pro since launch. It's definitely not a perfect solution (with buggy wake-from-sleep quite often) but it's a good compromise until there's native support.