My Nano T1 only has 1 HDMI connection, but it can support 3 screens. It has 4 USB SS connections. I’m not sure what a USB SS is. Does Ubuntu have info on setting up multiple displays?
Well, the display settings in the GNOME control center will show all displays it detected.
I would say this is more an hardware than a software issue.
You mention you only have one HDMI output. And unless your “USB SS” means USB C with DisplayPort capability, you won’t get a video signal out of them.
So that would, only by means of available outputs, limit you to one display.
And then the GPU has also to be able to drive multiple monitors at once which, considering the limited outputs, I wouldn’t take as a given.