Q: dynamic library issue on Mac OS X Catalina (A tail of two Catalinas) I have two Mac OS X Catalina systems (MacBook Air and iMac)
Both have Catalina.  The iMac is a fresh install.  The Air is an updater from years gone.
I have the same (as much as I can tell) dev environment on both.  xcode 12, xcode developer tools.
I have compiled an AGAR 1.6.1 (libagar) application on both.  I had all the same compile errors and issues on both systems which I managed to sort on both with the same solutions on both.  The libraries are .dylib (dynamic)
The application only runs on the MacBook Air and seg faults on the iMac.
Out of desperation I swapped the libagar libraries between the two systems and to my surprise the library still works on the MacBook Air and still fails on the iMac.
To clarify :
I took the working library on the Air and copied it to the iMac where it doesn't run and I took the broken library from the iMac and copied it to the Air where it does run.
So by process of elimination I think I can say the libraries are both OK and it has to be something with the underlying OS that is causing the application to seg fault.
What can I start looking at to try and find out what is different between these systems that is causing the library (and the app) to fail?
uname -a shows they are the same. Darwin 19.6.0
About Mac Says catalina 10.15.7 on both systems
otool -L  shows the libraries and versions are the same for both systems
