Yes I did follow the instructions, as stated in my OP. There is no difference between running ls /dev/tty* before and after cable plugin. No new device is added. I have no ttyACM device. Ran usermod command, then rebooted. No joy. running ls against all of /dev, I do find a usb directory (not ttyUSB) -- IDK if it relates to this problem.
This means your USB device doesn't have a device getting loaded/claimed for it (so nothing to do with CHIRP). Obviously the usermod/permissions stuff won't have any effect in that case.
You'll need to get a supported USB device/cable, or figure out how to load/assign a specific module for your cable if it's just a matter of it being mis-identified. How you do that will be distro and hardware-specific.
--Dan