Explain how?
Code evolvability is one of the extrinsic quality markers ( https://www.pathsensitive.com/2023/07/the-11-aspects-of-good... ).
If it's easy to add new features without creating bugs, the code is evolvable. Else, it's not. Does not seem very subjective.
Evolvability is not an intrinsic feature of the software. It is a synthesis of culture, talent, passion, and code style.
To use a simple analogy: you could argue that a modern Macbook is easier to maintain than an old Dell desktop, if the Macbook is owned by a certified Apple technician who knows how to microsolder, and the old Dell desktop is owned by someone who doesn't know how to use a screwdriver. But that doesn't change that, to change a hard drive, one needs much more skill and fancier tools than the other.