I have been playing AOE4 with 3 1080p monitors arranged 1tall x 3 wide with no issues. This was on a 960m passed through the intel igpu via a thunderbolt3 dock(2 DP and 1 HDMI). Not top tier performance but worked without issues for me.
I recently got an EGPU enclosure with a 1660 Super and tried to use full desktop mode with a 2 Tall x 3 Wide monitor configuration. It seems that it is not compatible with this arrangement. I can use windows to change the arrangement to 1x6 and it will work so I don’t think this is a hardware or setting issue with resolution or refresh rate. For this 3 are still through the igpu and the new 3 are directly connected to the 1660S.
I have attached a screen shot showing the full desktop with AOE running bottom middle and the rest of the monitors surrounding it.
I have tried changing just about all the options both in game and in the display settings of windows, Intel, and nVidia. If anyone has any trouble shooting Ideas I’m open to trying them.