Hello Bart,
Don't think Mendix does support it, you can raise it on the idea forum, however I think you could make it work yourself.
Both Nvidia and AMD graphic cards allow for your desktop to span across two displays through their graphics app, and with the Mendix app split across your two screens you can drag microflow/page windows to use only half the screen size (i.e. if your desktop spans across both display you'd be effectively using a single display for each side of the screen).
See below an example of the split midway on Mendix:
Hope this works for you.