Your screen shot says "Adapter Firmware Version". I'm not sure if that means active or passive.
I agree this, I do not think it is a real VGA port, should be digital to analog device, therefore I call it analog port is right.
I accept that Apple has made some changes. You're saying that the analog port will work in 10.11.x with a FB@ patch? I don't see any reason why an analog port wouldn't work in 10.11.x (with a small patch at most) since it's no different than HDMI or DisplayPort from the graphics chip perspective.
I use below patch for 0x19120000, and avoid to use 1030403 4 port patch.
FF000000 01000000 20000000 01050900 00040000 87010000 02040A00 00040000 87010000 03060A00 00040000 87010000
01050900 00080000 87010000 02040A00 02000000 87010000 03060A00 10000000 87010000 FF000000 01000000 20000000
Because analog port is mostly linked to F@ 0306 port 7, which is hidden in 10.11.x, 4 display patch can enable it with ig-platform-id 0x19120000, but 1030403 patch also caused some multi display problem.
In 10.12.x, 0x193b0005 is added, native support 4 ports, no patch is required.
I don't see how Apple could mess up a graphics driver like that. Are the two digital displays detected as different displays (different EDID contents)? Turn off display mirroring? They should have separate resolution lists. Use SwitchResX?
It should be EDID detect issue, I tested with both SwitchResX and ResXtreme, try to update system EDID information with those app but failed, 21:9 + 16:9 combination never success with DVI + HDMI configuration, my LG 21:9 need downscale to 16:9 for digital combination.
See attached png, captured in 10.11.6, LG Utrawide need downscale to 16:9.