In the HackberryPi CM5, does that pointing device (which IIUC is repurposed from Blackberry hardware) work like a joystick/TrackPoint?

Can you move smoothly at all angles with it, well enough to use the desktop GUI?

Yes. I tried to find a good video showing it, this one from the same creator shows it being used as a mouse and you can see it works pretty well: https://www.youtube.com/watch?v=568L-P2tBwc

Thanks for finding that. Nice. Starting at 14s in the video, looks like it's doing both coarse and fine movement. I don't know whether it would have to calibrated for best balance on the tiny display, but looks like it will probably work pretty well.