The reason why it’s Islamophobic and racist is because the vast majority of people who are supporting the Palestinians are Muslims.
It would therefore follow that as the majority of supporters are Muslim, they would also have the highest amount (as a percentage of the overall amount) of people who are anti-Semitic, because every race and religion weighing in will have a percentage of racists.
For example, there are 100,000 English Christians who support a cause and 1,000,000 Muslims who support the same cause. 1% of the English people would be 1,000 racists English people, but 1% of 1,000,000 Muslims would be 10,000 people. The percentage is the same, but you’d note the Muslims more, simply because of the numbers involved.
There are also plenty of Muslim majority countries who could not care less about the Palestinians, as well as Muslim nations who love Israel, like Azerbaijan, and even the United Arab Emirates booted someone out of a football match for bringing a Palestinian flag.
It really is a fallacy to conflate being Muslim as one homogenous race/thought machine.
There are 1.8 billion Muslims in the world, of every race and from widely varying cultures. There will be some countries that have history of wars with Israel that may make them feel negatively about Jewish people (like Jordan) and others are either supportive of Israel or fully neutral.