I just tried and I think they are limitations on numerous android OS.
It isn’t exactly a widget but what I have been able to do is create a shortcut when long pressing home assistant app icon on my phone
To do so, go to home assistant app settings/compagnon app/shortcut Give it a name and description, not too short according to documentation (see below), next add under dahsboard
Edit: added another screenshot from settings (sorry in french but that should help). This was just a quick test, this is why I named it assist_widget. You can also change icon type