In addition to the laptop screen, I plugged in an external monitor using the laptop's hdmi port. So far so, good.
I have a second external monitor (with the hdmi plugged into a port that then plugs into the USB-C port). The computer "sees" it: in the Display/Settings, the laptop and first external monitor come up as 1/3. The second monitor shows up as number 2, but it won't come on.
When I go to the Window's Display/Settings and highlight it, the computer asks me to pick various combinations of any TWO of the monitors--but never all three.
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