unable to copy to /usr/lib

Question

I am trying to copy a file to /usr/lib, but permissions are denied. SIP is disabled. When trying to copy via terminal, getting "Read-only file system".

Answer 1

This is correct behavior. You should not under any shipping OS be able to paste to that directory.

Much better to use a script or PATH or environment variables to extend your library in /usr/local/lib or other locations intended for customization. The OS manages the /usr/lib/ directory so your files will get stomped the next time an OS update happens or cause other breakage.