Very well done on making something so elegant! I use breadboards a lot, just for fun, even though I can solder just fine. I must admit though that I’m rarely so tidy with breadboards!
I fixed the problem of this compilation error on my iMAC now.
It may be caused by an unclean removal of the previous version of Arduino IDE on my iMAC when I upgrade to the new version 1.8,7.
There is a folder called ~/Library/Arduino15 holding all the board packages and preference.txt. I also found another folder holding the same thing : ~/Library/Arduino (probably left over from the old version).
I am not sure if this caused the issue.
After erasing everything in that folder ~/Library/Arduino15 and Library/Aruduino and getting a clean copy of Library/Arduino15 from my other MAC (very old MacBook air) that do not have this compilation error, I was able to compile successfully on my iMAC.
By the way, I live in Hong Kong. I got the parts for my projects through taobao (online shop of Alibaba) very quickly with cheap shipping. I used to create Crystal radio projects. But now work on MCU projects more.
Thanks again for taking the time to answer my questions.
Upgraded my breadboard with a hand soldered flash cart with SMD components.
I used 4Mbyte flash memory. Should be enough to hold 100+ games.
which is enough for me.