https://pressgazette.co.uk/publishers/nationals/guardian-steve-bell-cartoon-netanyahu/ this article goes into the past accusations a bit more, tbh I'm struggling to see it as well:

" The incident is not the first involving Bell, The Guardian and allegations of anti-Semitism against his cartoons. In 2018 he said he was censored by the newspaper’s editor, Katharine Viner, when the editorial team declined to publish a cartoon depicting a Palestinian medic shot dead by Israeli forces in a fireplace besides Netanyahu and then-prime minister Theresa May.

Bell subsequently sent the cartoon in an email to the entire Guardian editorial staff, from where it was leaked to Huffpost. Critics argued the image evoked Nazi gas chambers, which Bell responded was “the last thing on my mind when I drew it”.

Viner told The Guardian’s reader’s editor that Bell’s point “could easily have been made in a way that didn’t reference fire or ovens”.

In 2019, another of Bell’s cartoons – this time depicting Labour deputy leader Tom Watson as a witch hunter looking for anti-Semitic tropes – was blocked. In November 2020, The Guardian received 32 complaints of anti-Semitic imagery over a Bell cartoon which did make it to print and depicted Labour leader Keir Starmer holding the head of predecessor Jeremy Corbyn on a plate, alluding to the beheading of St John the Baptist. "

My understanding is that the cartoon is based on a cartoon of Lyndon B Johnson from decades ago. However, the cartoon uses the common metaphor of taking a "pound of flesh" from something to make it's point.

That metaphor is attributed the character Shylock from Shakespeare's Merchant of Venice. Shylock is considered by many to be an offensive stereotype of a Jewish person (I think it is) that is sort of "tolerated" when used in a historical context, but not otherwise. i.e. if you call a Jewish person "Shylock", expect rightly to be called a racist.

The cartoon applied to LBJ isn't offensive because, afaik, he isn't Jewish. But take the character and Netanyahu, smush them together and bam: antisemitism claims.