Amazon.com: ASUS ThunderboltEX 4 with Intel® Thunderbolt™ 4 JHL 8540 Controller, 2 USB Type-C Ports, up to 40Gb/s bi-Directional Bandwidth, DisplayPort 1.4 Support, up to 100W Quick Charge. : Electronics
StarTech.com Thunderbolt 3 to PCIe USB 3.1 Adapter - Chassis + 4 (BNDTBUSB3142)
Sonnet Thunderbolt 3 Upgrade Kit for the xMac mini