Wouldn't that just be "Raw"? I.e. start a webserver and ask the system to open the URL. There is no "special stuff" to do in this case like avoid sockets in favor of IPC to a well known webview or package CEF and no real integration to make with dev tools etc after - it's just open socket and serve from prebuilt binary.
No. As I understand it, the Raw backed just gives you a Window with input handling and you have to embed something like Skia, WebGPU for the graphics. So basically you have make your widget library yourself.
Now you can just start a server with deno pretty easily and serve a website. But WebUI will actually also manage opening the browser window for you as well a make the communication between backend and frontend just like using a Webview or electron.