Standardized firmware isn’t something that’s specified in the ISA, is it? It’s just shitty phone manufacturers.
Asus had some x86 phones a few years back. I haven’t dug into them, but I doubt they had a full bios/efi.
pine64 arm devices have u-boot, while a bootloader does fullfil a subset of the uefi spec.
I bought one years ago. Maybe 2018? I think it’s a kindle touch 8th gen, ad-supported. Cost me ~60€, ad-supported. It got jailbroken and KOReader installed. It has stayed offline since, so those ads have long since expired.
It gets the job done. I’ve never been in the amazon e-book ecosystem, and I don’t want to be licensing my books at their mercy.