I am running some test to help figure out what is going on so I thought I would pass that along with one question at the end.

I noticed that your installation webpage image of Visual Studio for installing Linux included an optional option called IntelliCode which is selected in the image. My Linux did not have that option. Is that an issue?   

Since you now say you can replicate it any ideas how to fix it?

Last night I closed VS2017 and deleted the .vs folder and this image show the result.

oops just noticed I can't add attachments again.

After loading the simple project, a squiggly at the very top of the code page says: 

"There are too many errors for the IntelliSense engine to function properly, some of which may not be visible in the editor".

IntelliSense does not work at all in this project.

After looking around in the solution folders I notice a file ".vaarduino.h" that is generated   automatically that includes <Arduino.>.

I'll look into the ArduinoJson duplicate files. In post #15 I included a step by step file containing different include files that demonstrate the same issue regardless of include files and boards.

Something else I noticed after reinstalling vMicro is the VS2017 Recent file list now shows two options for each sketch created. One is the ".sln" and the other is the ".vcxproj" file. What is causing this?
 
I just created a new empty project and the first thing I tried to do was to declare a String and IntelliSense reports it as undefined.

Creating an empty project in the Arduino 2.3.3 IDE does not cause this issue. String is defined and the project builds normally. Perhaps uninstalling and reinstalling the Arduino IDE might fix this?

Can I go back to the earlier version of vMicro that I was using? I checked my emails for the last renewals but they do not mention the version number I was using.

OK, I changed from ARM64 to ARM but the problem was still there until I changed the board from NodeMCU-32S to LOLIN(WEMOS) D1 R2 & mini. Now IntelliSense is working properly.

4 Questions 
(1) Why does my Resent file list show both the ".sln" and the ".vcxproj" files?

(2) Why does a breakpoint at void loop() randomly appear?

(3) How can I update my new email address to the sales department, so I'll be notified of my subscription renewal?   

(4) How will I be notified of the new update? Will you repost here when it is ready?

Thanks very much for your speedy help!

Thank you very much for your help!

Upgrading Visual Studio 2017 Professional is not an option at this time. 

Do you have an earlier version of Visual Micro that is compatible with Arduino 2 where the IntelliSense issue does not exist in VS 2017?

Is there a reason you cannot use VS2019 Community edition, or try the Trial Version in VS2022 Community?

After installing VS 2019 IntelliSense is now properly working.

Thanks