Late 2020 models of MacBook Air, MacBook Pro 13-inch, and Mac Mini systems using the original Apple M1 chip support only a single external display over the Thunderbolt 3 ports, even when connected to a Thunderbolt 3 docking station or adapter with more than one video output. This limitation also applies to using multiple Thunderbolt or Type C display adapters on both Type C ports.
This is not a limitation of StarTech.com products specifically, and Apple lists support for only one external display in the Tech Specs for Video Support on the M1 MacBook Pro 13” [external link to apple.com]. Turning off the laptop display or using clamshell mode does not change this.
One option for docking that allows more than one external display with an Apple M1-based Mac is to use a USB-C DisplayLink-based docking station or video adapter that requires a driver install. One dual monitor example is our DK30CHDDPPD, but please contact StarTech.com support for a recommendation based on your specific setup.
Please note: this single monitor limitation does not affect Intel-based Macs with Thunderbolt 3, or later M1 models that ship with M1 Max and M1 Pro processors.