No more system dylibs on the filesystem; only loadable with dlopen (from shipped dyld cache). The title is a shocker that sounds like system libraries are no longer dynamically linked...
Edit: Since this comment is currently at the top, here's a better link to the source: https://developer.apple.com/documentation/macos-release-note... (using scroll-to-text fragment[1] since there's unfortunately no usable anchor to the specific entry; not supported in non-Chromium browsers at the moment, in that case search for "built-in dynamic linker cache").