When Running rawtherapee-cli on MacOS Monterey 12.2.1 I get "Killed: 9"

First thing you might want to try is a newer version. The one you are using now is old and should not be used any longer.

You mention arm64, so you probably need the macOS (11.3) link. The zip file comes with an installable dmg file and the cli version (not a stand-alone item, do read the INSTALL.readme.rtf file).