Another one, desktop webviews don't exist either. Everyone does something custom right now and there's an epic vent fest in one of their GitHub issues. This causes about 1 new package to get released every few months too that tries to address it.
PlatformView support is one of our top desktop priorities this year (along with multi-window support).
https://pub.dev/packages/desktop_webview_window
Edit: on 2nd glance perhaps this doesn't embed into the widget tree but is always its own window?