@david_2018 posted a nice answer while I was writing this, but since there is some additional information here, I'll go ahead and post it anyway.
sevenoutpinball:
I don't know what the command line tool sed is
It's a Linux thing. I'm into that sort of thing for automation, but for this application I would prefer to just use a text editor to manually make the change. I use the command line all the time, but I also feel that a GUI is often a more intuitive way of getting things done. I'm not afraid of losing my "geek credentials" by not using the command line for every single thing.
sevenoutpinball:
Users/billbee/Documents/Arduino/libraries/MD_DS3231/src/MD_DS3231.h:763:18: error: expected ')' before '*' token
You will only get this error if you still have ENABLE_RTC_INSTANCE defined as 1.
Do this:
Open Users/billbee/Documents/Arduino/libraries/MD_DS3231/src/MD_DS3231.h in a text editor.
Change line 248 from:
[code]#define ENABLE_RTC_INSTANCE 1 ///< Enable default RTC instance creation
to:
#define ENABLE_RTC_INSTANCE 0 ///< Enable default RTC instance creation
Save the file.
Now you have have made the library so that it won't cause a name conflict with the RTC name already in use by the Uno WiFi Rev2's support software (for its built-in RTC). The next thing you need to do it modify the sketch to create an object of the MD_DS3231 class that also has a unique name (the example sketches use the conflicting "RTC" object name that you just configured the library to no longer create).
In your sketch, after the #include <MD_DS3231.h> line, add this line to create a MD_DS3231 object:
MD_DS3231 MD_RTC;
(or use any unique name you like in place of "MD_RTC")
Edit > Find...
In the "Find:" field, type RTC.
In the "Replace with:" field, type MD_RTC.
Click the "Replace All" button.
After that, you should be able to compile the sketch for the Uno WiFi Rev2. If this seemed like a lot of hassle and complexity, keep in mind that it would not have been necessary if you had chosen any of the other DS3231 libraries in the Arduino Library Manager.[/code]