In plain language
HDMI carries a +5V line that says “something is connected here”. A device watches that line to know whether a display is present. Force it off and the device stops seeing the downstream display at all.
Why it matters in your setup
That sounds like sabotage, and used carelessly it is. Used deliberately it is a diagnostic and a fix. It stops a display that sleeps, wakes slowly or drops out from disturbing the upstream negotiation, and it lets an emulated EDID stand entirely on its own rather than tracking the real sink.
It is also a clean test: if a fault disappears once the display is invisible, the display's own behaviour was part of the problem.
What the DR HDMI 8K does with it
TX +5V force is on by default on the DR HDMI 8K. Setting it to off means the display at the output is not detected by the unit, as if the HDMI cable were physically disconnected — while video keeps flowing. Combined with a fixed custom EDID, that gives you a source that sees exactly one stable display and nothing else.
Need the hardware?
Open the DR HDMI 8K product page on HDfury.uk.