CoreBox 4th i3-1215u

My USB-C Thunderbolt 4 connection has stopped working on the Chuwi CoreBox just shortly after I bought it from Chuwi store, in China. The Windows desktop is missing at the start. Windows 11 pro. start with a black screen and the cursor only. The thunderbolt controllers are already installed. My 4k LG Monitor and the same USB-C thunderbolt cable are functioning because I have tested them on my Intel Nuc PC. What might be the problem might? Could anyone help?

The Display Port and the HDMI connections are working.