The #NAME? error means that you have cells that refer to functions that are undefined. They are evidently in the extensions that you may have installed on Windows but are not in the version you installed on Mac. Please click on the cells individually to see if you can determine precisely which formulas are causing the problem. The _XLFN demonstrates that the Mac recognized an extension in a Windows version that it knew how to deal with; it did NOT know how to deal with at least some of the others.
Yes, IFS is a new function that only works with Excel 2016. I would imagine that an older version that may have automatically downloaded an upgrade plugin from somewhere might have to prefix the functions because they live in some external DLL. With the prefix specified, the function evaluation engine would know to look for the code in the appropriate OLE object rather than in the native function namespace.