A lot of functions are added to become more compatible to Microsoft Excel. They are written to file in the kind of "of:com.microsoft.foo". These functions do not belong to ODF1.2 but they are extensions done by LibreOffice.
Section 2.3.1 list item D in ODF 1.2 part 2 say, "Applications should clearly document their extensions in their user documentation, both online and paper, in a manner so users would be likely to be aware when they are using a non-standard extension."
Such documentation is missing for the com.microsoft.foo kind of functions. For example the functions STDEVP and STDEV.P have identical help texts. The user gets no hint that STDEVP is written as 'STDEVP' and is defined in ODF1.2, and that STDEV.P is written as 'COM.MICROSOFT.STDEV.P' and is not defined in ODF1.2. That is a large interoperability problem.
The OpenFormula extensions are documented in https://wiki.documentfoundation.org/Development/ODF_Implementer_Notes/List_of_LibreOffice_OpenFormula_Extensions
However, I agree we should have better / add more detailed information to the Function Wizard and/or online/wiki help.