An open-source alternative to QT for embedded devices

How do I talk to a serial port, CANbus driver, or GPIO registers on the target hardware? Can I read values directly from the SoC ports? Do I have filesystem access?

I'm curious how they define 'low-end device' here if it needs a javascript interpreter to run.

Watching the presentation at https://www.youtube.com/watch?v=27o_f_b1U3Q, it looks more like they're focused on making things like media players and settop boxes than, say, an IoT thermostat. And you'll need a Cortex-A class device or greater running Linux.