Would a custom ROM (eg. Lineage) also affected? (Score 1)

Folks, What are your thoughts on this still affecting a phone with a custom rom? I have a Xiaomi mi6 (which is great lilttle phone; 6gb, snapdragon 835 and still has an IR blaster) upgraded to Android 11 with a custom ROM (ShapeShiftOS from xda) - does replacing the OS with a nice open-source option prevent these spyware problems, or are they baked into the firmware? For example, some phone companies (huawei comes to mind) don't unlock the bootloader for their phones. With an unlocked bootloader you can root and really see what the phone is doing as well as replace the ROM. Some brave techies somewhere would probably dig in and find dodgy spyware code. I don't know enough to say if this is a red flag or not, or whether a firmware exploit would be undetectable regardless of OS, except possibly by packet capture. Curious, Q