Not being compatible with the Bonjour Network Service was the Issue! I had an old Asus WiFi router that booted up, and without connect internet to the router, I just did a WiFi connect ion to it on both my AVP and MacBook... and then Xcode Devices immediately recognized it.... and thus, I was able to proceed with setting the AVP to developer mode in Security settings.

Best that I can determine at this point, is that my Wi-Fi network is not compatible with Bonjour Network Service... i.e., which is mentioned in Apple Xcode Docs for "running you app on a device"... they mention "The Wi-Fi network must be compatible with Bonjour." I have not been able to find a method to check if it is Bonjour compatible, so will have to wait and try on a different WiFi network. Has anyone encountered this similar issue?

Some clarification on my post... the General Setting of "Remote Devices" occurs on the Apple Vision Pro. The MacBook Pro has no special settings that are required... i.e., one should simply be able to launch Xcode, open a project, select Window, Devices & Simulators, select Devices... and then you see you Vision Pro available as a device, and you enter the pairing code.