I’m starting to see not as many newer mobiles in the Lineage OS list as I used to. The US is a lost cause with companies not allowing their bootloader to be unlocked, but even the Chinese companies like OPPO, Vivo, OnePlus etc don’t seem to have their recent devices on the Lineage OS supported list. Am I imagining this, or is the Custom ROM market reducing to just Pixel phones?
No OEM to my knowledge provides BLOBs publicly.
LineageOS instead extracts these from the official ROM.
RE and/or shimming only need to happen when those BLOBs become incompatible with newer versions of Android.
The actual task of a maintainer is to configure the rather generic AOSP/LOS to work with the device’s specifics and integrate device-specific components.
For a few simpler examples, it must be configured which of a device’s SIM slots (if any) are eSIMs, which brightness values the device’s light sensor is expected to return, where the device has a fingerprint sensor (if it has one), the dimensions of the notch cutout and many other such things.
both google and Sony provide firmware blobs publicly, not sure about others.