I've read the article several times and still am having trouble. I have two monitors that connect to a docking station. One connects with an HDMI cord and the other with a DisplayPort. I can only get the two external monitors to mirror each other (mirror is not turned on) rather than act separately. When my Macbook Air 2019 is open I can use one of the monitors as a separate interface and the other just mirrors, and the MacBook acts as my second monitor. When I close the laptop, I only have the two mirrored displays on the external monitors and can't get them to act separately.
NOTE: My dock only has one HDMI cable port and two DisplayPorts. Might the problem be that I need 2 HDMI ports on my dock?
Thanks for any help you can provide.