https://ph.yhb.org.il/en/05-04-01/
The reason the Rambam does not include this mitzvah in his count of the 613 is that it is beyond the regular “value” of mitzvot; therefore, it is not included in their detailed enumeration. This coincides with the rules the Rambam lays down at the beginning of Sefer HaMitzvot,
stating it is inappropriate to reckon commandments that encompass the
entire Torah, as he writes in Mitzvah #153 [that settling the Land of
Israel is all-inclusive]. Besides which, it is implausible to say that
the mitzvah of Yishuv HaAretz is only rabbinically ordained today [and that that is why the Rambam leaves it out of the count]. After all, Chazal’s statement that settling the Land is equal to all the mitzvot
of the Torah was made after the destruction of the Second Temple. Now,
it is unlikely that they would say such a thing about a rabbinic mitzvah. Moreover, it is improbable that the Rabbis would dismantle a family (see above regarding divorce), and allow one to violate a shevut, merely for the sake of a rabbinic mitzvah (see Rabbi Zisberg’s Nachalat Ya’akov, Vol. 1, pp. 201-249).