In an earlier post I made about whether POC can be racist against each other, I think the problem was that my definition of racism was too narrow to account for other ways that racism is expressed. Thus, I define racism as not only the power to withhold or grant benefits that are not earned, but also the power to keep powerful/powerless relationships the same. In this case one good example I can think of that I wrote about for a final paper for my Asian Americans of Mixed Heritage class is whether Asian Americans using the word Hapa (a native Hawaiian word) to describe themselves is racist. I came to the conclusion that it is, because (tl;dr version) it robs the autonomy of native Hawaiians to use their own words as part of their own identity and misappropriates that word to describe another people which reinforces colonizer/colonized relationship of Asians to native Hawaiians (since they also worked under whites in the plantations and had higher standing above the native Hawaiians, regardless of not being equal to the whites).
Therefore it is possible for POC to be racist against each other if they buy into the negative (or even positive e.g. smart Asian) stereotypes that originate from white ignorant perspectives in order to other POC. This upholds the dominant paradigm of whites over POC. However it is not possible for POC to be (systemically) racist against whites since whites already are in the dominant/powerful position.