MultiMonitor: Mixing Fullscreen and Windowed

I am trying to find a way of mixing fullscreen and windowed using unity 5’s TargetDisplay system.

I have seen the page here:

It seems to be that activating a monitor causes all to go into fullscreen.
For example, I can’t fullscreen on the secondary and leave the primary monitor windowed.

It does seem like there is some combinations of resizing and activating windows that will allow you to mix fullscreen and non fullscreen. But it doesn’t seem consistent.
If i activate all of the displays then set the resolution of the primary monitor to be less than the native resolution, it will allow me to switch back and forth between a windowed primary monitor and full screen secondary monitors. The primary monitor doesn’t have window borders in this case. And seems to require setting sending the resize commands multiple times for it to fully catch.

Are there any suggestions for dealing with this? I am submitting it as a bug report because the behavior is undesirable, inconsistent, and even on a simple project with one script, messing around too much will crash the system.

I noticed it too in 2018.1.

The main screen will always go full screen.

You can resize other screens using SetParams but it’s windows only.
And be wary, if you try to force an unsupported resolution into a zone of the screen (it’s not actually windowed, it’s borderless of a fixed position and size) it will use the closest resolution supported to it and try to squeeze it into the region you asked for. Effectively skewing everything,

All in all, I find there are many options to go about regarding multi-display with Unity, sadly.

I have got quite similar problem.
If I use 1 display and one camera, the window title bar is visible. The window is movable and resizable.
But if I use 2 displays (one camera for each). All of them are border-less (no title bar), un-movable, un-resizable. Furthermore, the second display is always full screen.
I wonder how to make both displays are windowed, movable, and resizable.
Any help is appreciated.

Unity 2020.3.0f1.