The device formerly known as HUION Huion Tablet Pen stylus is now called HUION Huion Tablet stylus
Sleeping for two seconds solved the problem
I was mildly surprised to find two Displayport outputs
The new xf86-input-wacom package works just fine
The tablet cursor can fall into the crack between my landscape left monitor and portrait right monitor.
The solution turns out to be putting all the configuration options back in /etc/X11/xorg.conf, exactly where they started.
All in all, it’s much better than it was.