CRUD for what? Blocks have a CRUD framework for themselves. You could create a custom block that provides any kind of UI you want, so the answer is a qualified yes. How feasible it is depends on what the CRUD is for.
You can develop a CRM using REACT. It doesn’t really need to be contained within a block, but it’s feasible if that’s important for some reason. It sounds more like a page level app than a block level app to me. Either way, your app would likely want to achieve CRUD through the REST API.
