Nvidia Mosaic Limitations
The Nvidia Mosaic setup only supports output to an X * Y matrix of screens with similar resolution. Nvidia also recommends that all the screens in a Mosaic video wall should be the same model. One GPU can provide four outputs. It is not recommended to add more GPUs to the computer.
Using Datapath
The easiest way to configure for different screens is to use an external video wall display controller like Datapath Fx4. These controllers accept up to 4K input and 4 outputs. With Nvidia Mosaic up to 4 outputs from the GPU can be combined and split up with Datapath Fx4 display controllers.
See