Some widgets and modules, like Qt Charts (or Graphs, I forget), are dual GPL and commercially licensed, so it's a bit more complicated than that. You also need a commercial license for automotive and embedded deployments.
> You generally can't adhere to the LGPL in automotive
"Can't" or "won't"?
The UI process is not usually the part that need certification.
> Slint has a similar license
Indeed, but Slint's open source license is the GPL and not the LGPL. And its more permissive license is made for desktop apps and explicitly forbid embedded (so automotive)
> You also need a commercial license for automotive and embedded deployments.
How does that work? The LGPL (really any OSI license) isn't compatible with additional usage restrictions.