On Windows I usually launch external processes from the Shell using "system". ... Which is the best way to achieve the same in a script for macOS?

In theory it should be exactly the same (except for the .exe extension of course), system is cross-platform (with a few caveats, see system in perlport). Have you tried it, are you having any problems? If so, please post the exact error message along with a short piece of code needed to reproduce the error (an SSCCE).

BTW, you should check the return value of system for errors; it is also reflected in $? (but only rely on its value immediately after the call). I wrote at length about the topic of running external commands here.