OK, that was weird. Just a few weeks after praising my 2012 Mac Mini’s longevity, it decided to not recognize the 27″ QHD Benq monitor attached via DisplayPort.
Multiple reboots and turning the monitor on and off did nothing. Disconnecting and reconnecting cables did nothing.
On a whim I connected my Dell Windows laptop to the monitor via HDMI 2.0, and it worked. Switched the monitor back to Display Port, and voila, suddenly the Mac was connected and displaying full 2560 X 1440 resolution.
I don’t use the Mini for work, mostly just NetFlix and for the occasional Mac app, but it’s nice to have it back.