You need to read the fine print, as well as between the lines. From the IFS support page (click here):

What that means is: it is available as of "Excel 2016"
in Office 365, but not in a standalone version of Excel until Excel 2019.
The problem is with versioning of Excel in Office 365, IMHO. I don't use Office 365. But from what I've seen in this forum, Excel in Office 365 displayed version "Excel 2016" (and probably a later version now).
Office 365 gets updated frequently. (Not necessarily a good thing, IMHO..)
Standalone versions of Excel get updated only when a support package is released -- and even then, it is not guaranteed to keep pace with Office 365.
A year ago or so, I had read that MSFT promised to release a support package for standalone Excel 2016 that would include the new functions that MSFT made available in Office 365 before then. I don't know if that ever happened.
(I have Excel 2010, the last "good" version of Excel, IMHO.)