To install the DisplayLink Manager app, please follow these steps:
Download the latest driver: [displaylink] mac usb display adapter.zip
Connect the StarTech.com product to both your Mac and the external display
Follow Steps 4 to 4.10 here: DisplayLink Manager App for macOS [external link to DisplayLink.com]
If the displays still do not work, please review these points:
After installing, ensure you have completed Steps 4.4 to 4.9 in the linked article, which includes running the application after installation and selecting “Launch automatically after logging-in”.  This will ensure it starts automatically every time you log-in.
On Apple M1-based Macs, you may be prompted to install Rosetta during the DisplayLink install process. This is currently required to allow DisplayLink to work on Apple Silicon Macs.
Clamshell and rotation support on macOS Big Sur 11.x with DisplayLink Manager [external link to DisplayLink.com]