so I have attached an external monitor HDMI onto a Dell block to my laptop no problem, I have attempted to attach a 2nd portable monitor through the block type c cable to the block - when this connects the laptop does not recognise a 3rd screen, the portable screen turns on and disconnects the other screen, when I disconnect the portable screen the original external screen switches back
According to the specifications (linked below), there's one Thunderbolt port (which is likely what you're using to display video to the monitor that works), and two USB 3.0 ports (which will not support video output unless you attach an external video adapter). Example linked below.
