xhci-unsupported.kext works by injecting missing device IDs and configuration data, tricking macOS into loading its native xHCI driver for those otherwise unsupported controllers.
Here is a clear, concise text on the topic: Understanding xhci-unsupported.kext in Hackintosh USB Configuration xhci-unsupported.kext
xhci-unsupported.kext is a small but vital kernel extension (kext) used primarily in OpenCore or Clover bootloaders for Hackintosh systems. Its purpose is to enable compatibility between macOS and certain third-party USB 3.0 (xHCI) controllers that are not natively supported by Apple’s own AppleUSBXHCI driver. xhci-unsupported
Most Intel and AMD motherboards have USB controllers that work out of the box with macOS. However, some chipsets — especially older or less common ones (e.g., ASMedia, Etron, Fresco Logic, or certain Renesas controllers) — may fail to initialize properly. Symptoms include USB 3.0 ports not working, devices not being recognized, or system instability. Most Intel and AMD motherboards have USB controllers