It is imperative that you start by updating macOS to the latest version. Early versions of Big Sur would not load kernel extensions properly, so trying to install the driver on a system without the latest updates from Apple would be pointless.
Check and make sure you have the latest version of Big Sur.
Click on the Apple icon, then select System Preferences
Select Software Update
Allow the system to update to the latest version
After the operating system is completely up-to-date, please follow these step by step instructions to install the Thunderbolt driver on macOS 11 Big Sur or 12 Monterey.
Download driver from Lynx web site.
Open the ZIP file.
Open Installer Package: Lynx_macOS.pkg.
To accept the license agreement, click Continue
Next click Install
The driver will install automatically.
If the Macintosh has an M1 processor, you may be prompted to enable system extensions in the Recovery environment. If this not an M1 processor, or if system extensions have already been enabled, skip down to "System Extension Updated".
If so, click on Shutdown. and restart the Macintosh in the recovery environment by holding down the power key an continuing to hold down the power key until the recovery environment starts.
Click on Security Policy...
Select "Reduced Security" and make sure "Allow remote management of kernel extension and automatic software updates" is checked. PLEASE NOTE that you must leave the system set to Reduced Security permanently or the driver will not load. Next click on OK and restart the Macintosh.
You will see the "System Extension Updated" message, click on "Open Security Preferences"
The Security & Privacy page will display and shows that "System software from developer" needs to be allowed.
Click on the "Lock" icon to unlock the panel.
Next click on the "Allow" button to allow the driver to load. The system should prompt you to restart.
Click the "Not Now" button, then click the "Restart" button on the Installer package window.