NOTE: This computer problem ONLY came about because our house has the option to connect both WiFi and Ethernet connections to our computers.  I suspect that Apple changed their recent operating system to allow for this conflict.  Both  Wi-Fi and Ethernet to be turned on at the same time into your computer.

CAUTION:  The following descriptions and solutions can be rather difficult to understand.  If my explanations are not clear to you, do NOT attempt any of these changes.  If you attempt to make any changes to any computer settings, please write each change down so you can back out if things do not work better.

I have been using iMac (Retina 5K, 27-inch, 2019) for years and began having problems after the Big Sur software was provided (11.5.2).  Over time, I noticed that my iMac was acting very slow (probably unrelated to this main issue).  Then, all of a sudden my iMac failed to connect to the Internet.  It seemed that my problem was with our Internet cable provider.  I was wrong.  A technician came to our house and spent two hours evaluating our system and thinks that the Internet signal coming into the house was just a bit too weak.  He installed an amplifier to boost the signal coming into our house.  He got my iMac to work also by switching out a 1 by 3 with a 1 by 2 cable splitter.  He also was suspicious of our Macintosh Airport Time Capsule unit not performing properly.   But, the next day my iMac failed to show an Internet signal.  What is going on?  I did some research using my cell phone while having lunch with my wife at a restaurant.   The best advice I found, that helped me pinpoint this problem, was to disconnect every device from the iMac and reboot the computer.  Then see if all those disconnected devices made the computer work.  Well, the computer did work perfectly with all those cables removed.  I then reconnected each cable, one at a time, and restarted the computer to view the result.  I found that this pinpointed the problem exactly. I found out that when I connected my Ethernet cable to my iMac, the Internet failed.   I think this was because I always use WiFi to get Internet into my iMac.  So TWO Internet signals were flowing into my iMac.  This is rather odd.  You would think that Apple would have automated this not to happen.  My wife has an iMac and has BOTH WiFi going into her computer at the same time.  But she was told by her employer IT department NOT to upgrade her system until they checked it out for bugs.  So, she is using Catalina 10.15.7.   I went to her computer and discovered that I could NOT activate WiFi and Ethernet at the same time.  The Macintosh programmers with her system had avoided this conflict problem.  So, it seems that the newer update is possibly flawed on my computer.  If this is true, then over two hours of my cable system provider was wasted as well as hours of my time.

Troubleshooting method:

I used two applications to show me if there was a problem or not on my computer screen.  These two computer programs would definitely show me failure because both show very nice large windows on my computer screen:

1.  Airport Utility was important for showing me if we were getting the Internet cable provider signal or not.  At the top of the this display screen is a round globe, probably representing the Earth.  Just below this globe shows whether I am connected to the Internet or not.  The color dot before the word Internet is what you need to check.  Green is good WiFi connection.

 

2.  Ring Doorbell computer application was also pretty nice in that it was a go or no go revealing I had a problem or not.   This application would fail to show my Ring cameras and doorbell if my home WiFi input system failed.  I used both these empirical indicators as my test meters.  I had both these applications opened on my computer screen during all my tests.

Solutions:

1. Unplug the Ethernet Cale going into your computer.  This is the most simple solution.  This assumes that your WiFi is working and turned ON at your computer.  It also assumes that you favor Wi-Fi over Ethernet.  If you do not get a signal into your computer, then go into the System Preferences > Network and turn that port on (explained next).
2. The next solution is way more complicated and requires more steps to complete.  But, this system gives you more specific control, if you understand this process.  Go into your System Preferences by mouse clicking the apple logo in the top left corner of your screen.  Select System Preferences from the rather long drop down menu.  This will then show you a really large list of system operation options for you to modify.  Mouse click on the Network menu option.

Once Network is chosen, you should see all the individual signals going in and out of your computer.  In the image below, you can see that my computer had BOTH Ethernet and Wi-Fi turned on!  The solution was to turn OFF Ethernet and turn ON Wi-Fi.  It is my opinion that Apple programmers made a mistake by allowing both Ethernet and Wi-Fi to be active.  On my wife’s iMac, the programmers had solved this problem.

 

The above configuration was my problem because, as you can see BOTH Ethernet and Wi-Fi are connected!  I went into the menu and turned off Ethernet as seen in the image below.

The way you turn on and off any signal connection using this system preference is to look just below the list of connections where you will see this very small control panel at the bottom.  I enlarged this panel image below for you to identify it better.

 

The + is used to add a new signal.  (Do not use this right now)

The – is used to delete a signal source shown in the list above.  (Do not use this right now)  

The above menu item shown above is what you need to look at.

Mouse click on any signal input and this small menu item gives you the option to turn that signal OFF if it is currently ON.  It also allows you to turn that signal ON if it is currently OFF.  If Ethernet shows on the list, you can then turn it off.  I recommend that you do not remove it as you may want to turn it on some time in the future.  Make sure that WiFi is turn on if that is your favorite method for getting Internet.

OPTION: 
You can also reverse the above instructions and turn OFF WiFi and turn ON Ethernet.  It is your choice.  But, if you have my problem that the computer fails with both on, then make sure you choose one or the other.  

OPTION:
My house has both Ethernet and WiFi.  If your home system is the same BUT you have a failure with one of those systems, then go to your computer and make sure the signal system in your home that IS working is now turned on at your computer so your computer can continue to receive Internet signals.

 

 

Posted August 30, 2021