“Hard Yakka” Means Hard Work

In informal Australian English, “hard yakka” means strenuous, demanding work. It is not a kind of tool called “yakka”. Yakka comes from yaga, meaning “work” in the Yagara language of the Brisbane region. It entered Australian English in the nineteenth century and is now heard most often in the phrase hard yakka.

A: How was moving house? B: Hard yakka, but we got it done.

It suits talk about moving house, physical labour or any demanding task, and has a relaxed, distinctly local flavour. Yakka is generally uncountable, so do not say a hard yakka. In formal settings, or with people unfamiliar with Australian English, hard work is clearer.

https://history.cass.anu.edu.au/centres/andc/meanings-origins/all
https://www.abc.net.au/education/learn-english/learn-english-borrowed-aboriginal-words/8248664