Things start to break apart when you have dependencies that adopt newer standards or use broader features. There is only so much you can do unless you would like to reimplement libraries like SKIA, doctest, Qt6 or any modern game engine. It gets worse with security and updates. At some point a library will require a newer standard otherwise you have to adopt the entire codebase and assume the entire responsibility of all security updates.

At that point you are slowly rewriting the universe. So you can also do it in Rust tbh (which provides seamless updates and integration between epochs/editions).