Summary
Because the bootloader is locked, there is no active community of developers creating device-specific ROMs for the C100.
Here is everything you need to know about the current state of custom ROMs for the Nokia C100 The Reality of Custom ROMs for the C100 Currently, there are no official device-specific custom ROMs (like LineageOS) developed specifically for the Nokia C100 . However, because the Project Treble , you can technically install a Generic System Image (GSI) What is a GSI?
. Without an unlocked bootloader, you cannot flash custom recoveries like TWRP or ROMs like LineageOS Lack of Development