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.
Olivier Hallot committed a patch related to this issue. It has been pushed to "master": https://git.libreoffice.org/help/commit/830ed1f1dd5ad301e635f32f4120297fcb104000 tdf#94537 Inform user of non-ODFF functions (part)
Olivier Hallot committed a patch related to this issue. It has been pushed to "master": https://git.libreoffice.org/help/commit/7ad8f2bbd7b786557b8bcd9b275e0c312a921bf8 tdf#94537 COM.MICROSOFT.* namespace information
Olivier Hallot committed a patch related to this issue. It has been pushed to "master": https://git.libreoffice.org/help/commit/990e1236dc288bca7e7c8678353f505e9d1e9116 tdf#94537 ORG.OPENOFFICE.* namespace information
Olivier Hallot committed a patch related to this issue. It has been pushed to "master": https://git.libreoffice.org/help/commit/c7e7800abe70df5f14c03c63a829ed74d403a5fd tdf#94537 ORG.LIBREOFFICE.* namespace information
Olivier Hallot committed a patch related to this issue. It has been pushed to "master": https://git.libreoffice.org/help/commit/816284668c5fece9eaa275fb94899e8d57e2e502 tdf#94537 OPT_* functions help ID's