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.
Outside making it so you don't have to call to open the link yourself, I'm still not sure what could be integrated in the scenario. Deno can integrate with WebView because the WebView APIs were designed to allow external applications to have full control of the session. CEF (the Electron-like) approach works because Deno packages CEF & the APIs as part of the app itself, having even more control of everything. Browsers are meant to be in control of themselves or the user, and have had a long history of fighting malware trying to act otherwise.
They beat Tauri at their CEF support.
Webviews are a mistake in most cases. They're too platform-specific, and certain Webviews (Safari/Webkit) are buggy as hell, making platform support a nightmare. (Linux, ironically, is even worse due to how underbaked webviews are on the major desktop Linuces - Tauri is barely functional on Linux.)
Deno Desktop could be a real contender in this space. It's good to see more Electron alternatives.
Sciter SDK [1] contains scapp[.exe] - standalone Sciter engine that can be attached to HTML/CSS/JS bundle making standalone (single exe file) and portable executable. https://quark.sciter.com/ tool allows to compile such apps.
Size of "hello world" is a size of scapp.exe binary + size of compressed HTML/CSS/JS bundle.
On Windows scapp.exe is of ~14 Mb. On Linux ~18 Mb.
Linux version at startup detects GTK4, Wayland or X11 and uses those as windowing backends.
On all platforms Sciter provides out of the box: HTML/CSS/JS runtime, libuv based Node.JS alike runtime, GPU accelerated rendering, WebGL 3D runtime, JS built-in persistence (NoSQL DB).
It does not have TS compiler built-in as Deno, but that TS-to-JS compiler is better to be outside anyway as it is used only once - at app loading.