 Folks were added to React version 16.8 and they let you use a components state and other React features without having to write classes. I love them because I find that I write a lot less code and the code that I do write is a lot more expressive of what I want to have happen when other things occur on the page. The SharePoint framework has supported React 16.8 since SPFX v1.9.1 was released in August of 2019, but we still can't easily use hooks.