While true that the Israeli oppression of its Arab and Muslim minorities within its internationally recognised borders is not exactly the same as South African apartheid, the analogy credibly holds. The oppression of the Arab population under its occupation and the consistent collective punishment visited upon those captive populations outside its internationally recognized borders is a whole other kettle of fish. That Israel is an ethno-nationalist state that has many laws that privilege people of a given religion over another is fact [1]. Whether the level of state discrimination at this point constitutes apartheid is arguable. That one can make the argument is not antisemitic.
You can disagree about the extent, but it's stifling free speech to lump it under antisemitism and say you cannot bring it up. So credible, that a variety of Israeli leaders have warned against the very thing.[2]
And it is relevant. If you believe that South Africa during apartheid should be called out for its apartheid, then it IS relevant to bring it up. If the murder of Khashoggi by the Saudis tars their economic achievements, why shouldn't this?
Funnily enough, South Africa under apartheid was a plucky little country that withstood much indigenous aggression and had a world leading economy.
[1] https://www.adalah.org/en/content/view/7771
[2] https://en.wikipedia.org/wiki/Israel_and_the_apartheid_analo...