Given the state

const [messages, setMessages] = useState({
  ReactJS: [],
  NestJS: [],
  Typescript: [],
  MySQL: [],
  Neo4j: [],
  Redis: [],
  ELK: [],
  Docker: [],
  Kubernetes: [],
  AWS: [],
  SocketIO: [],
});

Then the following is a way to update a specific room via a roomKey identifier nested in the state object. In React when you update state you must always return a new object reference, and this includes any nested state/properties that are being updated. array.prototype.push mutates the original array, it doesn't create a new array reference for React purposes.

setMessages(messages => ({
  ...messages, // <-- shallow copy state
  // copy existing nested state array into new array and append new element
  [roomKey]: [...messages[roomKey], newMessage],
}));

An alternative to the array literal is to use array.prototype.concat, which does return a new array.

setMessages(messages => ({
  ...messages, // <-- shallow copy state
  // copy existing nested state array into new array and append new element
  [roomKey]: messages[roomKey].concat(newMessage),
}));

Note: This assumes your roomKey variable will reference one of the keys actually defined in your state. If you use an unspecified key then messages[unknownKey] will be undefined. In this case, if you've truly dynamic keys, then you can provide a fallback value to spread into state.

setMessages(messages => ({
  ...messages, // <-- shallow copy state
  // copy existing nested state array into new array and append new element
  [roomKey]: [
    ...messages[roomKey] || [], // <-- provide fallback
    newMessage,
  ],
}));