I never heard of Milei until he won this election. When I hear the word “libertarian” (small-l), I think of Rand Paul and Ron Paul. I agree with small-l-libertarians on fiscal policy and the proper role of government. However, over the past 15 years or so, the capital-L’s took their party in a different direction.
Milei sounds more like a capital-L. According to Wikipedia, he’s made some interesting comments about “free love” and his participation in “threesomes.” I wouldn’t want someone like him for president. If he’d run for office here, he wouldn’t have gotten my vote, but it will be interesting to see where his small-l fiscal policies take Argentina.
You will be happy to learn that a group called the "Mises Caucus" has taken over the Libertarian Party. Since last year they have taken all of the leadership positions and are very right-leaning. They identify as followers of the Ron Paul revolution.
CATO, Reason and the old guard Libertarians are referred to as "beltway Libertarians" by the people who are now running the LP.