Bukele : Has stood up to US imperialism and its bully boy minions (e.g. the IMF). Wants El Salvador's wealth to be used for the betterment of the country and its people.

Milei : Is an obvious treasonous agent for US imperialism, the longest in a very long line of such agents. Will sell out Argentina in the old fashioned way by privatising public assets for cheap acquisition by foreign interests (mainly Western) and betray his country and further impoverish its people. Plus he's a creep and a loathsome Zionist.

So the two are chalk & cheese and anyone who thinks there's commonality between them is very politically naive.