There’s a reason SLI is dead. CPUs are fast enough that they can send the data to 2 or more video cards, along with viewport information, so they can render, for example, 2 side-by-side views with an X offset for the right view that is the width of the left view.
Before, CPUs weren’t fast enough to do this. And neither were GPUs.
Most of the render pipeline nowadays IS the GPUs. No, MSFS isn’t splitting off the data - but the underlying Windows graphics engine IS doing exactly that - feeding slightly different info to each GPU, because THAT part of Windows knows the physical dimensions and placement of each window to be rendered. The actual rendering is ALMOST ALL done in the GPUs nowadays.
Anyway, anyone who wants to can find out why SLI is pretty much dead nowadays. Nobody wants it with the much improved hardware - welcome to the 2020s.