From a high-level: the Iranian state hasn’t apologised for the 1970s US/Iran hostage crisis, nor its stated anti-Israeli position (see also: AIPAC lobbying), but most ostensibly because the IRGC continues to fund terrorism around the world - especially against US, European, Israeli, and Saudi interests.

SA escapes criticism because ostensibly they’re an ally(TM) of Israel and the US - and SA hasn’t committed state-sponsored acts of terrorism against western interests (9/11 wasn’t backed by the Saudi state - just by non-executive members of the extended royal family) and the economic and geopolitical leverage they get by being hosts of large numbers of US bases and getting OPEC to agree to use the Petrodollar which cemented the US at the centre of the world’s economy.

Well, has U.S. ever apologized for operation Ajax? https://en.wikipedia.org/wiki/1953_Iranian_coup_d%27état

"the Iranian state hasn’t apologised for the 1970s US/Iran hostage crisis"

This. The USA takes a looong time to forgive countries that humiliate it (or that it perceives to have humiliated it). I can't see any other reason for the USA to so strongly favour the headchoppers of SA over the headchoppers of Iran; they both have lots of ahl.

[Edit: the SA headchoppers are friends of Israel, the Iran headchoppers are friends of Hezbollah. So maybe it's to do with the evangelical obsession with the Rapture, and the return of all Jews to biblical Israel; I don't know if that was a thing back in Carter's day.]

But Iran should had forgiven the toppling of its legitimate president?

Their country their business. They don't need to apologize to anyone for ousting a dictator no matter who they chose to replace him with.

No, I mean this: https://en.wikipedia.org/wiki/1953_Iranian_coup_d%27%C3%A9ta...