Funny story about this. A Sr. SWE on my team - let's call him Sam - gained quite a bit of notoriety in our org division by doing this.
The core "backend", used by teams all across the division, is a giant C++ project (~1 million LOC) that used to be compiled with a Makefile that would recursively call other Makefiles. It was very brittle, obfuscated, inflexible, and a huge pain point. But also a huge endeavor to change build toolchains.
Sam worked part-time for about 2 years converting the build system into CMake. He met with many stakeholders of the project, along with engineers on teams that wrote clients for the backend. The end result was a significantly more robust, performant, and portable build for everyone.
It dramatically increased his profile in the company, and was quite impressive to witness.