My main question is if you can use Thunderbolt 3 external HDD enclosures over the USB 4.0 Ports. Although I wonder about other Thunderbolt devices
The usb 4 ports use the Intel Mapleridge(JHL8540) Thunderbolt 4 controller and the ports are the 40 speed USB4 option. Also Thunderbolt drivers are installed on setup. The only thing I could see that would make it not fully TB4 compliant is if it provides the lower 7.5 watt vs TB4 minimum of 15watt or due to dual monitor support.
They could have implemented the Ports non Thunderbolt spec. My guess would be that it doesn't meet the wattage requirements for full Thunderbolt 4 or it's a resolution issue. It does utilize the full PCIe3.0 x4 lanes though. Here is what I've found so far. https://imgur.com/a/GwkI5dd