tl;dr: This is a rambly post about trying to get a Virtual Monitor setup to work with a multi monitor display.
Fought with monitors tonight. Couldn't get a second monitor to work (Display Port). I've been using a UHD hdmi monitor for the last two weeks. Even after unplugging the HDMI and only running the DP, nothing would show up. Since the UHD is a smart tv, every time I unplug/replug the monitor, it decides to screw with it and go into detect the device mode. Mind you, when it does this, the screen comes up normal like it always has for about 3 seconds, then that gets hidden by the detection software of the smart tv, which eventually decides it is a 4096x2160 that I don't want fit to screen so it should display the center 3840x2160 pixels. Now I know how to get to the setting that doesn't fit to screen... but then... if the 4096x2160 is fit to screen, that means it doesn't actually display that size... then why is it reporting to Windows that it can if it is faking that size? Looking at it, I can't tell if anything is stretched or not.
So three restarts later I've got 2 Display Port monitors and an UHD HDMI monitor. Index still throws a 108 with "Last USB device malfunctioned) error, so that doesn't appear to be solved by getting the DPs working. But now, DisplayFussion's taskbars are fighting with Window's taskbars for which should be displayed and how. I've got DF's settings set to use the UHD as a 2 by 2 virtual monitors which does good for maximizing to quadrants of the UHD, and has split up taskbars for these 4 Virtual Monitors (VMs), but now every 10 seconds or so, the taskbars flash back and forth as windows things "Wait... isn't the main bar suppose to be across the entire bottom? and isn't the second monitor's bar supposed to be on top?" and DF replies "No Windows, the main taskbar is supposed to be the bottom left VM, and that's it. Stay on your half of the bottom of the UHD."
Found a post from 5 years ago asking NVidia to handle virtual monitors at the hardware level, telling windows "Yea... I've got 4 screens here, each 1920x1080 in a 2x2 square" and then let windows dictate what happens on these multiple monitors, allowing full screen, toolbars and windows to appear as separate screens, and NVidia pushing those displays out as the one UHD. This is the way to use UHDs. A seamless multi monitor. (I don't have a link to that post, as that was a week ago that I read it).
One of the things that DisplayFussion doesn't do right is the windows key + arrow keys. On a monitor, this means "move to this half of the screen", but in Virtual Monitors, it pushes it to the VM on that side, instead of that half of the VM.
Virtual Display Manager V3 is another Virtual Monitor tool. It doesn't do toolbars, but does one up DF in the full screen of a youtube video department. DF's VM full screen takes up the full UHD. VDMv3 correctly full screens to the given VM.
The bottom of my screen is still flickering, even after returning to 3840x2160 without fit to screen. I don't _think_ it's been there all this time.