Today() should have failed.  There isn't a Today() function.

There is Now() which will give you the current Date and Time
and Date()  Which will give you the current Date only.

I don't know what you are doing with conditional formatting using the above.  Access may be assuming that you created your own Today() function.  Case doesn't matter.  Access will convert it.

Try putting it in a query to try it out like below then run the query.  You will get an error (ON THE LEFT)

The Date() and Now() produce the results (ON THE RIGHT)

FYI - I just inserted CustomerT because you have to have a table in the query to test things.  You get a result for each customer in the table.

What are you trying to accomplish in your conditional formatting?
Maybe post a Screenshot to show us so we can help.  See Image Uploads if you don't know how.

Today() is an Excel function. Also used in VB.NET.