Numbers 20:1

The entire community. The entire, perfect community. Those who were to die in the desert had already perished, and these were set apart to live.

Miriam died there. Why is the portion concerning Miriam’s death adjacent to the portion of the parah adumah? To teach you that, just as the sacrifices bring atonement, so do the deaths of the righteous bring atonement.

Miriam died there. She, too, died by the Divine kiss. Why, then, is it not said, concerning her, “by the mouth of God”? Because this would be lacking in reverence toward the Supreme Being. Concerning Aharon, however, it is said, “by the mouth of God,” in “these are the journeys.”

And the whole congregation of the children of Israel came to the desert of Zin on the tenth day of the month Nisan. And Miriam died there, and was buried there.

In the first month. In the fortieth year, for the Torah includes no incident or prophecy that was not either in the first year or the fortieth year.

AND THE CHILDREN OF ISRAEL, EVEN THE WHOLE CONGREGATION, CAME INTO THE WILDERNESS OF ZIN. “The congregation — an upright congregation, for those who were [punished] with death in the wilderness [on account of sinning in the matter of the spies] had already died, and these were designated to live” [i.e., they were the new generation which was to enter the Land]. This is Rashi’s language, and such is also the opinion of Rabbi Abraham ibn Ezra. But if so, why was it necessary to mention this [same expression: even the whole congregation] when they came afterwards unto Mount Hor?. Now Rabbi Abraham ibn Ezra wrote [there] that Scripture mentioned it because Edom had come out to fight them,, Verse 20. therefore it mentions that none of them was missing when they came back from the city of Edom. But this is not correct, since Israel turned away from him [Edom], Verse 21. and did not wage battle with them at all.
The correct interpretation appears to me to be that it is the Scriptural style to mention [“the whole congregation”] when speaking of complaints, [just as in the following verses]: And all the congregation of the children of Israel came unto the wilderness of Sin, which is between Elim and Sinai;, Verses 2-3, that they murmured for food. And all the congregation of the children of Israel journeyed from the wilderness of Sin, by their stages … and encamped in Rephidim, 17:1. There too it is related in Verses 2-3 that they quarrelled with Moses, saying, “Give us water.” — and Scripture thereby informs us that they all [participated] in the complaint. Similarly, And all the congregation lifted up their voice; And on the morrow all the congregation of the children of Israel murmured. 17:6. There they complained about the death of Korach and his followers. Scripture uses that expression when they came to Mount Hor in order to tell us that they all took part in the mourning for Aaron, the holy one of the Eternal, just as it is said, and they wept for Aaron … all the house of Israel, and it states [furthermore]: in the sight of all the congregation., Verse 27. In Bamidbar Sinai Rabbah I have seen mentioned the text [quoted above by Rashi] — “an upright congregation etc.” — only in connection with the second verse [speaking] about Mount Hor [i.e., Verses 22 and 27 quoted above, which say that ‘the whole congregation came’ to Mount Hor, and that Moses and Aaron went up into Mount Hor ‘in the sight of all the congregation’], for in the case of the first verse [i.e., the present verse, the expression all the congregation] is used because [Scripture wants to indicate that they all joined in] the murmuring, as I have explained.

ותמת שם מרים, in the first month (Nissan) of the fortieth year. Aaron died after her in the fifth month as detailed in Numbers 33,38.