If removing the physical connector achieves the exact result you’re looking for, might it just be easier to get, or build, some manual on-off/disconnect toggles?
If you can’t find purpose-built options, and you aren’t comfortable building your own, maybe a manual toggle box for HDMI that you can switch to an empty port, as needed.
Alternatively, what about a script, or macro, to switch to mirror mode, and back again?
Haha nice, I’m glad I threw that in at the bottom lol.
If you do end up needing to do something physical, and can’t find a prefabricated item, look at getting 2 female HDMI breakout boards/connectors.
I believe there’s 19 wires in total, but only two deal with power (+/-) and 1 that deals with clock signal (tmds?). Could probably move those over to 3 pin on/off toggle switch, directly wire the rest, and then flip the switch as needed.
Or even just the TMDS wire 1 pin toggle switch, might even do the trick.
Those pinouts might be different based on the HDMI version you’re using, and I cannot stress this enough, I pulled that idea mostly out of my ass. I have some experience with this type of DIY, but none of it was with HDMI signals.
It is not intended as a final blueprint, just a starting point you figuring out a DIY toggle.