Do the Ben Ish Chai, or other Sephardic Chakhamim speak on the recitation of "Modeh Ani" upon rising in the morning? One so-called Rabbi of the West African Jews of the Galut says that "Modeh Ani" is not obligatory or required to say, because it was not stated in the Talmud or the Rambam and other Sephardic Chakhamim.
The modeh ani prayer is not mentioned in the Talmud or the Rambam.
It is first mentioned (as far as I can tell) in the Seder Hayom of Rabbi Moshe ben Machir who I believe was Sephardic himself.
It is present in the siddur of Rabbi Eliyahu Benamozegh (Sephardic rabbi who lived in Italy in the 19th century).
It is also referenced by Rabbi Shemual Alush (also of Tunisia) here.
Although the prayer seems to have only originated in the 16th century, it was evidently adopted by different Sephardic communities in different parts of the world.
It should be noted that the recitation of this prayer is a custom; not an obligation, whether one is Sephardic, or part of any other group of Jews.