Oh my god!, I have done it.
Thanks upfront to all support you guys gave me here, and the will not to give up on this....I found it....my thought was correct.
I searched the web and found the necesseray correct ArduinoOTA version for my old MBP verison and processor.
It was 1.4.1 and here is the victory screenshot...
I'm glad it is working now. Thanks for taking the time to share your findings!
Surprisingly, it does seem to be an incompatibility with macOS 12 specifically:
Even though that information mentions macOS 12 specifically, I assumed that was only due to that being the latest version of macOS at the time it was written, and expected the true situation to be an incompatibility between old versions of Go and versions of macOS >=12. However, I just gave arduinoOTA 1.3.0 a try on my macOS 26 ("Tahoe") machine and it worked fine.
As you discovered, the latest 1.4.1 release of arduinoOTA was built using Go 1.17, and so does not have the problem of incompatibility with macOS 12. Unfortunately the "Arduino AVR Boards" platform specifies a dependency on arduinoOTA version 1.3.0, and so you get this outdated version when you install arduinoOTA via the "Arduino AVR Boards" platform installation, even though a more modern version of the tool is available.
