To understand the reality of a custom ROM for the Nokia 23, one must first define the device itself. While model numbers vary by region, devices like the Nokia 230, 215, or the hypothetical "Nokia 23" fall firmly into the category of "Feature Phones" running the S30+ operating system. Unlike smartphones that utilize open-source operating systems like Android, S30+ is a proprietary, closed-source real-time operating system (RTOS). It is designed for stability, minimal battery consumption, and basic telephony, not for user customization.
: You may find Generic System Images (GSIs) —like the LineageOS 23 GSI nokia 23 custom rom