The cause is just that the panel is mounted rotated on the device. It's supposed to be used in a tablet where the top is the short end and the side is the long end, opposite to a laptop.

Somewhat common with Chuwi and GPD's netbook type devices. IIRC it's because they repurpose tablet screens

Yes, I did, and the reason is super straightforward: It's a hardware portrait panel, mounted sideways.

Getting from zero to a fully working OS was a mild journey, but I'd do it again.