You need to bind your event handler to your class component as below

 import React, { Component, useImperativeHandle } from 'react';

 class SearchBar extends Component {
   constructor(props) {
     super(props);
     this.onInputChange = this.onInputChangebind(this); //You NEEDED THIS
  }
   
  render() {
    return <input onChange={this.onInputChange} />;
  }
  onInputChange(event) {
    console.log(event)
  }
  }

export default SearchBar;

Works on my side... i highlighted the console.log outputs as shown on picture

otherwise if you needed to see the words you typed on the input tag you can just do console.log(event.target.value) instead of console.log(event)