I’m not confusing binaries and OS, but I never flashed full A12 OS here, just A12 binaries. So this last experiment was “A12 binaries on top of A11 OS”.
“Binaries don’t change anything” I should’ve worded better: A12 binaries on top of A11 OS caused a camera functionality regression. Everything else seemed to have stayed equal to my A11 binaries experience, hence no reason to try fix the camera regression in some other way.
I flashed A11 binaries back: Android camera functionality was immediately restored.
Thanks for SFOS partitions backup/restore guide: I will do a full A12 base flash after I’m back from US road trip, avoiding large risks during travel.
(US: where X10III lack of band 12 is definitely sub-optimal, see Sailfish in the USA - #244 by lkraav)