Create an Output Window

Take that literal. Create one and only one output window (Window COMP), no matter how many outputs you want to connect (provided all outputs are connected to one computer). Is all you need and if you open more than one window you pay with performance. This window should cover all the screen estate that you want to use.

Use the same technique as described in the last Topic to arrange your contents onto the available screen estate. You can feed every operator to the Window COMP to display the node-display in the window. Best practise however is to arrange your different contents (usually outputs and preview/interface) as panels in a container and use that container to feed the Window COMP.

If you want to know more about the monitors/outputs that TouchDesigner sees,
you could use a Monitor DAT, notice how it not only tells you the resolution and refresh rate of the monitors but also their position in the overall screen estate.

Dont worry, it is usually not that complicated.
Most of the time you only need to care about two monitors.