Note: I just restored my Omega to factory defaults (by pressing and holding the reset button on the Dock). The Omega can successfully join my home Wi-Fi network, which is a 2.4 GHz Apple AirPort Extreme router. After it joined, I typed "oupgrade" to check for latest firmware. Result:
Device Firmware Version: 0.2.2 b200
Checking latest version online...
Repo Firmware Version: 0.2.2 b200
Comparing version numbers
Device firmware is up to date!
However, the problem described in my original post persists. My macOS 10.14.6 computers can see the Omega's Wi-Fi AP network (which has the default name, "Omega-1979" and password "12345678"), but they cannot join it.
So ... help!