And now I read this:
System Integrity Protection (SIP) was disabled ... csrutil status ... boot into the recovery mode... hold ⌘-R when booting ... open a terminal ...type csrutil enable and reboot ... DisplayPort-to-mDP2 cable to connect to the Thunderbolt 2 port ... get a Thunderbolt 3 to Thunderbolt 2 dongle ... Thunderbolt 2 means 4 PCI Express 2.0 lanes with DisplayPort 1.2 ... Change the monitor to MST mode ... recover via HDMI ... Apple Digital AV Adapter ... HDMI instead of mDP2 ... third-party DisplayPort adapter ...
And so on and so on. "Just works"?