If I understand the concept of IQ correctly, you can learn pretty much everything even with a low IQ, it will just take more time.
The reason why it's hard for English speakers is because Chinese is so different than English. Our brains learn more easily things that are similar to things we already know. This is why you will have an easier time learning Spanish than Chinese if you're an English speaker. It also has to do with how much you got exposed to Spanish compared to Chinese.
It's worth nothing that East Asians struggle with English very much because for them English is so different than their own languages.
After learning Chinese for a while you start to grasp some things more quickly - because it became something you already know. A few times I also found tiny things in Chinese that are similar to English or even to my native language Hebrew, which is pretty weird but cool.
Everyone can learn Chinese, it can take more or less time for you but it doesn't really matter. It's a fun journey!