It’s also still under “experimental”
Also: Why not simply make your center monitor the primary display in Windows? You can show/drag your taskbar on another screen or have that taskbar shown on all screens.
Edit:
I just did a few tests here (3 monitor setup) and I really can’t see what your problem is. If you drag your central MSFS screen to the middle monitor, make it full screen via Alt+Enter, you can then just enable to additional screens left and right of it. Despite the right monitor being the primary monitor.