Why is "Il lui envoie deux mille roses". "He set HER" 2000 roses. Could it not also mean he sent HIM?

Bonjour Fran !

Indeed, in French the indirect object pronoun for "him" and "her" is lui. Here, only the context can let you know whether the referrent is masculine or feminine.
We simply picked one :)

https://progress.lawlessfrench.com/revision/grammar/when-to-use-lui-and-leur-to-replace-specific-people-with-him-her-and-them-indirect-object-pronouns

Bonne journée !