How to fix black screen?

Question

Windows

Good day. Has HP T610 PLUS Flexible Thin Client
Processor AMD Dual-Core T56N
Video - Radeon HD 6320, Embedded OS -
Windows 10. LTSC
DFMirage driver is not installed on the TightVNC server. (tomorrow I will check)

There are 2 DisplayPort connectors.
When I disconnect the DisplayPort cable from this PC, the Tightvnc client starts showing a stupid black screen, although the mouse runs, the keyboard shortcuts work. It can be seen later, when connecting the DisplayPort cable back.

Someone tell me how to win this?